Bug: Remove inline attribute for platform_use_identity_mmu_mappings()

Making the function inline forces every file that includes it to use
the function. A warning is flagged otherwise.

This also requires the compiler.h to be included as this
has the #define for __ALWAYS_INLINE.
diff --git a/include/platform.h b/include/platform.h
index e052851..191077e 100755
--- a/include/platform.h
+++ b/include/platform.h
@@ -36,7 +36,7 @@
 void platform_init(void);
 
 /* called by the arch init code to get the platform to set up any mmu mappings it may need */
-inline __ALWAYS_INLINE int platform_use_identity_mmu_mappings(void);
+int platform_use_identity_mmu_mappings(void);
 void platform_init_mmu_mappings(void);
 addr_t platform_get_virt_to_phys_mapping(addr_t virt_addr);
 addr_t platform_get_phys_to_virt_mapping(addr_t phys_addr);