soc: nuvoton: Add SoC info driver for WPCM450

Add a SoC information driver for Nuvoton WPCM450 SoCs. It provides
information such as the SoC revision.

Usage example:

# grep . /sys/devices/soc0/*
/sys/devices/soc0/family:Nuvoton NPCM
/sys/devices/soc0/revision:A3
/sys/devices/soc0/soc_id:WPCM450

Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Reviewed-by: Paul Menzel <pmenzel@molgen.mpg.de>
Link: https://lore.kernel.org/r/20221031223926.241641-1-j.neuschaefer@gmx.net
Signed-off-by: Joel Stanley <joel@jms.id.au>
Link: https://lore.kernel.org/r/20230201051717.1005938-1-joel@jms.id.au
Signed-off-by: Arnd Bergmann <arnd@arndb.de>