soc: amlogic: gx pm domain: add PM and OF dependencies

The new driver introduces harmless warnings:

warning: (PM_RMOBILE && ARCH_RCAR_GEN1 && ARCH_RCAR_GEN2 && ARCH_R7S72100 && MESON_GX_PM_DOMAINS) selects PM_GENERIC_DOMAINS which has unmet direct dependencies (PM)
warning: (MESON_GX_PM_DOMAINS) selects PM_GENERIC_DOMAINS_OF which has unmet direct dependencies (PM_GENERIC_DOMAINS && OF)

This adds CONFIG_OF and CONFIG_PM dependencies to ensure it
will only be enabled in valid configurations.

Fixes: 75fcb5ca ("soc: amlogic: add Meson GX VPU Domains driver")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>