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/css/drivers/mhu/css_mhu.c b/plat/arm/css/drivers/mhu/css_mhu.c
index 30492a6..7b33317 100644
--- a/plat/arm/css/drivers/mhu/css_mhu.c
+++ b/plat/arm/css/drivers/mhu/css_mhu.c
@@ -81,7 +81,7 @@
 	arm_lock_release();
 }
 
-void mhu_secure_init(void)
+void __init mhu_secure_init(void)
 {
 	arm_lock_init();
 
@@ -93,7 +93,7 @@
 	assert(mmio_read_32(PLAT_CSS_MHU_BASE + CPU_INTR_S_STAT) == 0);
 }
 
-void plat_arm_pwrc_setup(void)
+void __init plat_arm_pwrc_setup(void)
 {
 	mhu_secure_init();
 }