sched/stats: Print domain name in /proc/schedstat

Currently, there does not exist a straightforward way to extract the
names of the sched domains and match them to the per-cpu domain entry in
/proc/schedstat other than looking at the debugfs files which are only
visible after enabling "verbose" debug after commit 34320745dfc9
("sched/debug: Put sched/domains files under the verbose flag")

Since tools like `perf sched stats`[1] require displaying per-domain
information in user friendly manner, display the names of sched domain,
alongside their level in /proc/schedstat.

Domain names also makes the /proc/schedstat data unambiguous when some
of the cpus are offline. For example, on a 128 cpus AMD Zen3 machine
where CPU0 and CPU64 are SMT siblings and CPU64 is offline:

Before:
    cpu0 ...
    domain0 ...
    domain1 ...
    cpu1 ...
    domain0 ...
    domain1 ...
    domain2 ...

After:
    cpu0 ...
    domain0 MC ...
    domain1 PKG ...
    cpu1 ...
    domain0 SMT ...
    domain1 MC ...
    domain2 PKG ...

[1] https://lore.kernel.org/lkml/20241122084452.1064968-1-swapnil.sapkal@amd.com/

Signed-off-by: K Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: Ravi Bangoria <ravi.bangoria@amd.com>
Signed-off-by: Swapnil Sapkal <swapnil.sapkal@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: James Clark <james.clark@linaro.org>
Link: https://lore.kernel.org/r/20241220063224.17767-6-swapnil.sapkal@amd.com

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