plat/arm/sgi: reorganize platform macros

In preparation of adding support for upcoming SGI platforms, macros
common to all the SGI platforms are moved into sgi_base_platform_def.h
file. Macros that are specific to sgi575 platform remain in the
platform_def.h file. In addition to this, the platform_def.h file is
moved to sgi575 board directory. Also the ENT_CPU_SOURCES has been
renamed to SGI_CPU_SOURCES and moved from sgi-common.mk to board
specific makefile platform.mk

Change-Id: Iccdd9f070f4feea232b9fbf4fdcc0ef2e8eccbf2
Signed-off-by: Chandni Cherukuri <chandni.cherukuri@arm.com>
diff --git a/plat/arm/css/sgi/sgi-common.mk b/plat/arm/css/sgi/sgi-common.mk
index 24f03dd..b6383aa 100644
--- a/plat/arm/css/sgi/sgi-common.mk
+++ b/plat/arm/css/sgi/sgi-common.mk
@@ -22,8 +22,6 @@
 
 PLAT_INCLUDES		+=	-I${CSS_ENT_BASE}/include
 
-ENT_CPU_SOURCES		:=	lib/cpus/aarch64/cortex_a75.S
-
 ENT_GIC_SOURCES		:=	drivers/arm/gic/common/gic_common.c	\
 				drivers/arm/gic/v3/gicv3_main.c		\
 				drivers/arm/gic/v3/gicv3_helpers.c	\
@@ -36,15 +34,13 @@
 				${CSS_ENT_BASE}/aarch64/sgi_helper.S
 
 BL1_SOURCES		+=	${INTERCONNECT_SOURCES}			\
-				${ENT_CPU_SOURCES}			\
 				${CSS_ENT_BASE}/sgi_bl1_setup.c	\
 				${CSS_ENT_BASE}/sgi_plat_config.c
 
 BL2_SOURCES		+=	${CSS_ENT_BASE}/sgi_security.c		\
 				${CSS_ENT_BASE}/sgi_image_load.c
 
-BL31_SOURCES		+=	${ENT_CPU_SOURCES}			\
-				${INTERCONNECT_SOURCES}			\
+BL31_SOURCES		+=	${INTERCONNECT_SOURCES}			\
 				${ENT_GIC_SOURCES}			\
 				${CSS_ENT_BASE}/sgi_bl31_setup.c	\
 				${CSS_ENT_BASE}/sgi_topology.c	\