ARM: fix misplaced arch_virt_to_idmap()

Olof Johansson reported:

In file included from arch/arm/include/asm/page.h:163:0,
                 from include/linux/mm_types.h:16,
                 from include/linux/sched.h:24,
                 from arch/arm/kernel/asm-offsets.c:13:
arch/arm/include/asm/memory.h: In function '__virt_to_idmap':
arch/arm/include/asm/memory.h:300:6: error: 'arch_virt_to_idmap' undeclared (first use in this function)

caused by arch_virt_to_idmap being placed inside a different
preprocessor conditional to its user.  Move it along side its user.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/include/asm/memory.h

@@ -174,7 +174,6 @@
 #define __PV_BITS_31_24	0x81000000
 #define __PV_BITS_7_0	0x81
 
-extern phys_addr_t (*arch_virt_to_idmap) (unsigned long x);
 extern u64 __pv_phys_offset;
 extern u64 __pv_offset;
 extern void fixup_pv_table(const void *, unsigned long);
@@ -290,6 +289,8 @@ static inline void *phys_to_virt(phys_addr_t x)
 #define __va(x)			((void *)__phys_to_virt((phys_addr_t)(x)))
 #define pfn_to_kaddr(pfn)	__va((pfn) << PAGE_SHIFT)
 
+extern phys_addr_t (*arch_virt_to_idmap)(unsigned long x);
+
 /*
  * These are for systems that have a hardware interconnect supported alias of
  * physical memory for idmap purposes.  Most cases should leave these