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/scp/css_pm_scmi.c b/plat/arm/css/drivers/scp/css_pm_scmi.c
index 258c1c2..d280101 100644
--- a/plat/arm/css/drivers/scp/css_pm_scmi.c
+++ b/plat/arm/css/drivers/scp/css_pm_scmi.c
@@ -328,7 +328,7 @@
 	return 0;
 }
 
-void plat_arm_pwrc_setup(void)
+void __init plat_arm_pwrc_setup(void)
 {
 	channel.info = &plat_css_scmi_plat_info;
 	channel.lock = ARM_LOCK_GET_INSTANCE;