AArch32: Add ARM platform changes in BL1

This patch adds ARM platform changes in BL1 for AArch32 state.
It also enables building of BL1 for ARCH=aarch32.

Change-Id: I079be81a93d027f37b0f7d8bb474b1252bb4cf48
diff --git a/plat/arm/common/arm_common.mk b/plat/arm/common/arm_common.mk
index 51bd60c..875e919 100644
--- a/plat/arm/common/arm_common.mk
+++ b/plat/arm/common/arm_common.mk
@@ -116,7 +116,7 @@
 				drivers/io/io_storage.c				\
 				plat/arm/common/arm_bl1_setup.c			\
 				plat/arm/common/arm_io_storage.c		\
-				plat/common/aarch64/platform_up_stack.S
+				plat/common/${ARCH}/platform_up_stack.S
 ifdef EL3_PAYLOAD_BASE
 # Need the arm_program_trusted_mailbox() function to release secondary CPUs from
 # their holding pen