peci: npcm: add nuvoton,npcm845-peci compatible

NPCM8xx device trees describe the PECI controller as
"nuvoton,npcm845-peci". The block is programmed the same way as on
NPCM7xx, but the driver only matches "nuvoton,npcm750-peci", so it
never probes on NPCM845 BMCs.

Add the new compatible. The PECI voltage select bit is also in the
same place (GCR INTCR3 at 0x9c, bit 19), which is what the upstream
driver (drivers/peci/controller/peci-npcm.c) uses for both SoCs. So
the GCR handling is shared: look up the SoC-specific GCR syscon, fall
back to the "nuvoton,sysgcr" phandle, and set PECIVSEL based on
"high-volt-range".

Change-Id: Ib85049c9f1f5b9492bf22fd054eb5b950b166bbc
Signed-off-by: William A. Kennington III <wak@google.com>