alif/Makefile: Allow specifying a custom build directory.

Signed-off-by: Damien George <damien@micropython.org>

Author: dpgeorge

ports/alif/Makefile

@@ -82,10 +82,10 @@ $(BUILD):
 	$(MKDIR) -p $@
 
 $(BUILD)/M55_HP/firmware.bin:
-	make -f alif.mk MCU_CORE=M55_HP MICROPY_PY_OPENAMP_MODE=0
+	make -f alif.mk BUILD=$(BUILD)/M55_HP MCU_CORE=M55_HP MICROPY_PY_OPENAMP_MODE=0
 
 $(BUILD)/M55_HE/firmware.bin:
-	make -f alif.mk MCU_CORE=M55_HE MICROPY_PY_OPENAMP_MODE=1
+	make -f alif.mk BUILD=$(BUILD)/M55_HE MCU_CORE=M55_HE MICROPY_PY_OPENAMP_MODE=1
 
 $(BUILD)/$(ALIF_TOC_CONFIG): mcu/$(ALIF_TOC_CONFIG).in | $(BUILD)
 	$(ECHO) "Preprocess toc config $@"

ports/alif/alif.mk

@@ -3,7 +3,6 @@
 
 BOARD ?= ALIF_ENSEMBLE
 BOARD_DIR ?= boards/$(BOARD)
-BUILD ?= build-$(BOARD)/$(MCU_CORE)
 
 ifeq ($(wildcard $(BOARD_DIR)/.),)
 $(error Invalid BOARD specified: $(BOARD_DIR))