plat/arm: Mark arm platform initialization functions

Mark the initialization functions found in the BL31 boot sequence
as __init so they can be reclaimed when no longer needed.

Change-Id: I687a89346419c7710ef5097feaa325d83c527697
Signed-off-by: Daniel Boulby <daniel.boulby@arm.com>
diff --git a/plat/arm/common/arm_common.c b/plat/arm/common/arm_common.c
index 28ff5d9..ae06ef2 100644
--- a/plat/arm/common/arm_common.c
+++ b/plat/arm/common/arm_common.c
@@ -41,7 +41,7 @@
  * - Coherent memory region, if applicable.
  */
 
-void arm_setup_page_tables(const mmap_region_t bl_regions[],
+void __init arm_setup_page_tables(const mmap_region_t bl_regions[],
 			   const mmap_region_t plat_regions[])
 {
 #if LOG_LEVEL >= LOG_LEVEL_VERBOSE