Use abspath to dereference $BUILD_BASE

If the user tries to change BUILD_BASE to put the build products outside
the build tree the compile will fail due to hard coded assumptions that
$BUILD_BASE is a relative path. Fix by using $(abspath $(BUILD_BASE))
to rationalize to an absolute path every time and remove the relative
path assumptions.

This patch also adds documentation that BUILD_BASE can be specified by
the user.

Signed-off-by: Grant Likely <grant.likely@arm.com>
Signed-off-by: Manish Pandey <manish.pandey2@arm.com>
Change-Id: Ib1af874de658484aaffc672f30029b852d2489c8
diff --git a/plat/marvell/armada/a8k/common/ble/ble.mk b/plat/marvell/armada/a8k/common/ble/ble.mk
index 82ac098..60fbf5f 100644
--- a/plat/marvell/armada/a8k/common/ble/ble.mk
+++ b/plat/marvell/armada/a8k/common/ble/ble.mk
@@ -5,9 +5,9 @@
 
 MV_DDR_PATH		?=	drivers/marvell/mv_ddr
 
-MV_DDR_LIB		= 	$(CURDIR)/$(BUILD_PLAT)/ble/mv_ddr_lib.a
-LIBC_LIB		=	$(CURDIR)/$(BUILD_PLAT)/lib/libc.a
-BLE_LIBS		= 	$(MV_DDR_LIB) $(LIBC_LIB)
+MV_DDR_LIB		=	$(BUILD_PLAT)/ble/mv_ddr_lib.a
+LIBC_LIB		=	$(BUILD_PLAT)/lib/libc.a
+BLE_LIBS		=	$(MV_DDR_LIB) $(LIBC_LIB)
 PLAT_MARVELL		=	plat/marvell/armada
 
 BLE_SOURCES		+= 	$(BLE_PATH)/ble_main.c				\
@@ -29,4 +29,4 @@
 FORCE:
 
 $(MV_DDR_LIB): FORCE
-	@+make -C $(MV_DDR_PATH) --no-print-directory PLAT_INCLUDES="$(PLAT_INCLUDES)" PLATFORM=$(PLAT) ARCH=AARCH64 OBJ_DIR=$(CURDIR)/$(BUILD_PLAT)/ble
+	@+make -C $(MV_DDR_PATH) --no-print-directory PLAT_INCLUDES="$(PLAT_INCLUDES)" PLATFORM=$(PLAT) ARCH=AARCH64 OBJ_DIR=$(BUILD_PLAT)/ble