ARM: samsung: move pm check code to drivers/soc

This is the only part of plat-samsung that is really
shared between the s3c and s5p ports. Moving it to
drivers/soc/ lets us make them completely independent.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20200806182059.2431-16-krzk@kernel.org


Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>