ARM: armv7: guard memory reserve for PSCI with #ifdef CONFIG_ARMV7_PSCI

If CONFIG_ARMV7_NONSEC is enabled, the linker script requires
CONFIG_ARMV7_PSCI_NR_CPUS regardless of CONFIG_ARMV7_PSCI.

Reviewed-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>