ARM: move outer_cache declaration out of ifdef

Move the outer_cache declaration of the CONFIG_OUTER_CACHE ifdef so that
outer_cache can be used inside IS_ENABLED condition.
Signed-off-by: Rob Herring <rob.herring@calxeda.com>
Cc: Russell King <linux@arm.linux.org.uk>

(cherry picked from commit 0b53c11d)
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>

arch/arm/include/asm/outercache.h

@@ -37,10 +37,10 @@ struct outer_cache_fns {
 	void (*resume)(void);
 };
 
-#ifdef CONFIG_OUTER_CACHE
-
 extern struct outer_cache_fns outer_cache;
 
+#ifdef CONFIG_OUTER_CACHE
+
 static inline void outer_inv_range(phys_addr_t start, phys_addr_t end)
 {
 	if (outer_cache.inv_range)