ARM: add psci_arch_init() declaration for CONFIG_ARMV7_PSCI

arch/arm/include/asm/system.h declares psci_arch_init(), but it is
surrounded by #ifdef CONFIG_ARMV8_PSCI.

psci_arch_init() is called for CONFIG_ARMV7_PSCI too. Add the missing
function declaration.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

arch/arm/include/asm/system.h

@@ -528,6 +528,7 @@ void mmu_page_table_flush(unsigned long start, unsigned long stop);
 
 #ifdef CONFIG_ARMV7_PSCI
 void psci_arch_cpu_entry(void);
+void psci_arch_init(void);
 u32 psci_version(void);
 s32 psci_features(u32 function_id, u32 psci_fid);
 s32 psci_cpu_off(void);