plat/arm/sgi: refactor the inclusion of memory mapping

Upcoming RD platforms have a different memory map from those of the
existing platforms. So make the build of the existing mmap entries to be
usable only for existing platforms and let upcoming platforms define
a different set of mmap entries.

Change-Id: Id1ef0293efe8749c78a99237e78d32573c7233aa
Signed-off-by: Aditya Angadi <aditya.angadi@arm.com>
diff --git a/plat/arm/css/sgi/sgi-common.mk b/plat/arm/css/sgi/sgi-common.mk
index 6b9e0cd..615f53d 100644
--- a/plat/arm/css/sgi/sgi-common.mk
+++ b/plat/arm/css/sgi/sgi-common.mk
@@ -32,8 +32,7 @@
 				plat/common/plat_gicv3.c	\
 				plat/arm/common/arm_gicv3.c
 
-PLAT_BL_COMMON_SOURCES	+=	${CSS_ENT_BASE}/sgi_plat.c	\
-				${CSS_ENT_BASE}/aarch64/sgi_helper.S
+PLAT_BL_COMMON_SOURCES	+=	${CSS_ENT_BASE}/aarch64/sgi_helper.S
 
 BL1_SOURCES		+=	${INTERCONNECT_SOURCES}			\
 				drivers/arm/sbsa/sbsa.c