arm64: dts: rockchip: Split up RK3588's PCIe pinctrls

These pinctrls manage the low-speed PCIe signals:
- CLKREQ#: An output on the RK3588 (both RC or EP modes), used to
  request that external clock-generation circuitry provide a clock.
- PERST#: An input on the RK3588 in EP mode, used to detect a reset
  signal from the RC. In RC mode, the hardware does not use this signal:
  Linux itself generates it by putting the pin in GPIO mode.
- WAKE#: In EP mode, this is an output; in RC mode, this is an input.

Each of these signals serves a distinct purpose, and more importantly,
PERST# should not be muxed when the RK3588 is in the RC role. Bundling
them together in pinctrl groups prevents proper use: indeed, almost none
of the current board-specific .dts files make any use of them.
(Exception: Rock 5A recently had a patch land that misuses _pins; this
 patch corrects that.)

However, on some RK3588 boards, the PCIe 3 controller will indefinitely
stall the boot if CLKREQ# is not muxed (details in the next patch).
This patch unbundles the signals to allow them to be used.

Signed-off-by: Sam Edwards <CFSworks@gmail.com>
Link: https://lore.kernel.org/r/20240912025034.180233-2-CFSworks@gmail.com
Signed-off-by: Heiko Stuebner <heiko@sntech.de>

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