AArch32: Add ARM platform changes in BL2

This patch adds ARM platform changes in BL2 for AArch32 state.
It instantiates a descriptor array for ARM platforms describing
image and entrypoint information for `SCP_BL2`, `BL32` and `BL33`.
It also enables building of BL2 for ARCH=aarch32.

Change-Id: I60dc7a284311eceba401fc789311c50ac746c51e
diff --git a/plat/arm/common/arm_common.mk b/plat/arm/common/arm_common.mk
index 875e919..98d7219 100644
--- a/plat/arm/common/arm_common.mk
+++ b/plat/arm/common/arm_common.mk
@@ -128,7 +128,7 @@
 				drivers/io/io_storage.c				\
 				plat/arm/common/arm_bl2_setup.c			\
 				plat/arm/common/arm_io_storage.c		\
-				plat/common/aarch64/platform_up_stack.S
+				plat/common/${ARCH}/platform_up_stack.S
 ifeq (${LOAD_IMAGE_V2},1)
 BL2_SOURCES		+=	plat/arm/common/${ARCH}/arm_bl2_mem_params_desc.c\
 				plat/arm/common/arm_image_load.c		\