plat: pass -D option to BL*_CPPFLAGS instead of BL*_CFLAGS

-D is a preprocessor flag that defines a macro. So, adding it to
BL*_CPPFLAGS makes more sense. You can reference it not only from
.c files but also from .S files.

Change-Id: Ib4f2f27a3ed3eae476a6a32da7ab5225ad0649de
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
diff --git a/plat/arm/board/rdn1edge/platform.mk b/plat/arm/board/rdn1edge/platform.mk
index 135676d..571d651 100644
--- a/plat/arm/board/rdn1edge/platform.mk
+++ b/plat/arm/board/rdn1edge/platform.mk
@@ -36,7 +36,7 @@
 endif
 
 # Enable dynamic addition of MMAP regions in BL31
-BL31_CFLAGS		+=	-DPLAT_XLAT_TABLES_DYNAMIC=1
+BL31_CPPFLAGS		+=	-DPLAT_XLAT_TABLES_DYNAMIC=1
 
 # Add the FDT_SOURCES and options for Dynamic Config
 FDT_SOURCES		+=	${RDN1EDGE_BASE}/fdts/${PLAT}_fw_config.dts