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/sgi/sgi_interconnect.c b/plat/arm/css/sgi/sgi_interconnect.c
index f4e7676..325b5b1 100644
--- a/plat/arm/css/sgi/sgi_interconnect.c
+++ b/plat/arm/css/sgi/sgi_interconnect.c
@@ -17,7 +17,7 @@
 /******************************************************************************
  * Helper function to initialize ARM interconnect driver.
  *****************************************************************************/
-void plat_arm_interconnect_init(void)
+void __init plat_arm_interconnect_init(void)
 {
 }