Build: introduce ${BUILD_PLAT} target to create the top build directory

Some platforms (for ex. UniPhier) want to create files in the very
top of the build directory.  Add ${BUILD_PLAT} so such files can
depend on it.

Make existing directory targets depend on ${BUILD_PLAT} because
they are sub-directories of ${BUILD_PLAT}.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

Makefile

@@ -260,6 +260,8 @@ include lib/stack_protector/stack_protector.mk
 
 include ${PLAT_MAKEFILE_FULL}
 
+$(eval $(call MAKE_PREREQ_DIR,${BUILD_PLAT}))
+
 # Platform compatibility is not supported in AArch32
 ifneq (${ARCH},aarch32)
 # If the platform has not defined ENABLE_PLAT_COMPAT, then enable it by default

make_helpers/build_macros.mk

@@ -291,7 +291,7 @@ define MAKE_BL
 
 # Create generators for object directory structure
 
-$(eval $(call MAKE_PREREQ_DIR,${BUILD_DIR},))
+$(eval $(call MAKE_PREREQ_DIR,${BUILD_DIR},${BUILD_PLAT}))
 
 $(eval $(foreach objd,${OBJ_DIRS},$(call MAKE_PREREQ_DIR,${objd},${BUILD_DIR})))
 

plat/rockchip/rk3399/platform.mk

@@ -88,7 +88,7 @@ ${RK_PLAT_SOC}/drivers/pmu/pmu_fw.c: $(RK3399M0FW)
 ${BUILD_PLAT}/bl31/cdn_dp.o: CCACHE_EXTRAFILES=$(HDCPFW)
 ${RK_PLAT_SOC}/drivers/dp/cdn_dp.c: $(HDCPFW)
 
-$(eval $(call MAKE_PREREQ_DIR,${BUILD_M0},))
+$(eval $(call MAKE_PREREQ_DIR,${BUILD_M0},${BUILD_PLAT}))
 .PHONY: $(RK3399M0FW)
 $(RK3399M0FW): | ${BUILD_M0}
 	$(MAKE) -C ${RK_PLAT_SOC}/drivers/m0 BUILD=$(abspath ${BUILD_PLAT}/m0)