fix(arm): use PLAT instead of TARGET_PLATFORM

There might be several platforms which use the
TARGET_PLATFORM build option to differentiate the code
between the platform variants.

Use of TARGET_PLATFORM in the common code leads to build
failures instead use PLAT build option.

Signed-off-by: Chandni Cherukuri <chandni.cherukuri@arm.com>
Change-Id: I9724caf875bd56225e035ecffa8b9ca1a50d3401
diff --git a/plat/arm/common/arm_common.mk b/plat/arm/common/arm_common.mk
index 3236596..064ed57 100644
--- a/plat/arm/common/arm_common.mk
+++ b/plat/arm/common/arm_common.mk
@@ -282,7 +282,7 @@
 ifeq (${JUNO_AARCH32_EL3_RUNTIME},1)
 BL2_SOURCES		+=	plat/arm/common/aarch32/arm_bl2_mem_params_desc.c
 else
-ifeq ($(filter ${TARGET_PLATFORM}, fpga fvp),)
+ifneq (${PLAT}, diphda)
 BL2_SOURCES		+=	plat/arm/common/${ARCH}/arm_bl2_mem_params_desc.c
 endif
 endif