bpf: use register liveness information for func_states_equal

Liveness analysis DFA computes a set of registers live before each
instruction. Leverage this information to skip comparison of dead
registers in func_states_equal(). This helps with convergance of
iterator processing loops, as bpf_reg_state->live marks can't be used
when loops are processed.

This has certain performance impact for selftests, here is a veristat
listing using `-f "insns_pct>5" -f "!insns<200"`

selftests:

File                  Program                        States (A)  States (B)  States  (DIFF)
--------------------  -----------------------------  ----------  ----------  --------------
arena_htab.bpf.o      arena_htab_llvm                        37          35     -2 (-5.41%)
arena_htab_asm.bpf.o  arena_htab_asm                         37          33    -4 (-10.81%)
arena_list.bpf.o      arena_list_add                         37          22   -15 (-40.54%)
dynptr_success.bpf.o  test_dynptr_copy                       22          16    -6 (-27.27%)
dynptr_success.bpf.o  test_dynptr_copy_xdp                   68          58   -10 (-14.71%)
iters.bpf.o           checkpoint_states_deletion            918          40  -878 (-95.64%)
iters.bpf.o           clean_live_states                     136          66   -70 (-51.47%)
iters.bpf.o           iter_nested_deeply_iters               43          37    -6 (-13.95%)
iters.bpf.o           iter_nested_iters                      72          62   -10 (-13.89%)
iters.bpf.o           iter_pass_iter_ptr_to_subprog          30          26    -4 (-13.33%)
iters.bpf.o           iter_subprog_iters                     68          59    -9 (-13.24%)
iters.bpf.o           loop_state_deps2                       35          32     -3 (-8.57%)
iters_css.bpf.o       iter_css_for_each                      32          29     -3 (-9.38%)
pyperf600_iter.bpf.o  on_event                              286         192   -94 (-32.87%)

Total progs: 3578
Old success: 2061
New success: 2061
States diff min:  -95.64%
States diff max:    0.00%
-100 .. -90  %: 1
 -55 .. -45  %: 3
 -45 .. -35  %: 2
 -35 .. -25  %: 5
 -20 .. -10  %: 12
 -10 .. 0    %: 6

sched_ext:

File               Program                 States (A)  States (B)  States   (DIFF)
-----------------  ----------------------  ----------  ----------  ---------------
bpf.bpf.o          lavd_dispatch                 8950        7065  -1885 (-21.06%)
bpf.bpf.o          lavd_init                      516         480     -36 (-6.98%)
bpf.bpf.o          layered_dispatch               662         501   -161 (-24.32%)
bpf.bpf.o          layered_dump                   298         237    -61 (-20.47%)
bpf.bpf.o          layered_init                   523         423   -100 (-19.12%)
bpf.bpf.o          layered_init_task               24          22      -2 (-8.33%)
bpf.bpf.o          layered_runnable               151         125    -26 (-17.22%)
bpf.bpf.o          p2dq_dispatch                   66          53    -13 (-19.70%)
bpf.bpf.o          p2dq_init                      170         142    -28 (-16.47%)
bpf.bpf.o          refresh_layer_cpumasks         120          78    -42 (-35.00%)
bpf.bpf.o          rustland_init                   37          34      -3 (-8.11%)
bpf.bpf.o          rustland_init                   37          34      -3 (-8.11%)
bpf.bpf.o          rusty_select_cpu               125         108    -17 (-13.60%)
scx_central.bpf.o  central_dispatch                59          43    -16 (-27.12%)
scx_central.bpf.o  central_init                    39          28    -11 (-28.21%)
scx_nest.bpf.o     nest_init                       58          51     -7 (-12.07%)
scx_pair.bpf.o     pair_dispatch                  142         111    -31 (-21.83%)
scx_qmap.bpf.o     qmap_dispatch                  174         141    -33 (-18.97%)
scx_qmap.bpf.o     qmap_init                      768         654   -114 (-14.84%)

Total progs: 216
Old success: 186
New success: 186
States diff min:  -35.00%
States diff max:    0.00%
 -35 .. -25  %: 3
 -25 .. -20  %: 6
 -20 .. -15  %: 6
 -15 .. -5   %: 7
  -5 .. 0    %: 6

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20250304195024.2478889-5-eddyz87@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

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