feat(plat/marvell/a8k): allow overriding default paths

The common makefile used by every a8k/cn913x platform
(a8k_common.mk) assumed default paths in PLAT_INCLUDES,
BLE/BL31_PORTING_SOURCES. Allow overriding those
variables, in order to avoid code duplication.

It can be helpful in case using multiple board variants
or sharing common settings between different platforms.

Change-Id: Idce603e44ed04d99fb1e3e11a2bb395d552e2bf7
Signed-off-by: Marcin Wojtas <mw@semihalf.com>

plat/marvell/armada/a8k/common/a8k_common.mk

@@ -80,7 +80,7 @@ MARVELL_GIC_SOURCES	:=	drivers/arm/gic/common/gic_common.c	\
 				drivers/arm/gic/v2/gicv2_helpers.c	\
 				plat/common/plat_gicv2.c
 
-PLAT_INCLUDES		:=	-I$(BOARD_DIR)				\
+PLAT_INCLUDES		+=	-I$(BOARD_DIR)				\
 				-I$(BOARD_DIR)/board			\
 				-I$(CURDIR)/drivers/marvell		\
 				-I$(PLAT_COMMON_BASE)/include		\
@@ -89,8 +89,10 @@ PLAT_INCLUDES		:=	-I$(BOARD_DIR)				\
 PLAT_BL_COMMON_SOURCES	:=	$(PLAT_COMMON_BASE)/aarch64/a8k_common.c \
 				drivers/ti/uart/aarch64/16550_console.S
 
+ifndef BLE_PORTING_SOURCES
 BLE_PORTING_SOURCES	:=	$(BOARD_DIR)/board/dram_port.c \
 				$(BOARD_DIR)/board/marvell_plat_config.c
+endif
 
 MARVELL_MOCHI_DRV	+=	$(MARVELL_DRV_BASE)/mochi/cp110_setup.c
 
@@ -125,7 +127,9 @@ ifeq (${MSS_SUPPORT}, 1)
 MARVELL_DRV		+=	$(MARVELL_DRV_BASE)/mg_conf_cm3/mg_conf_cm3.c
 endif
 
+ifndef BL31_PORTING_SOURCES
 BL31_PORTING_SOURCES	:=	$(BOARD_DIR)/board/marvell_plat_config.c
+endif
 
 ifeq ($(SYSTEM_POWER_SUPPORT),1)
 BL31_PORTING_SOURCES	+=	$(BOARD_DIR)/board/system_power.c