Add ARCH_SUPPORT_PSCI as a non-configurable option that platforms
can select.  Then, move CONFIG_ARMV7_PSCI, which is automatically
enabled if both ARMV7_NONSEC and ARCH_SUPPORT_PSCI are enabled.
Reviewed-by: NAlexander Graf <agraf@suse.de>
Signed-off-by: NMasahiro Yamada <yamada.masahiro@socionext.com>