esp8266: Allow to override serial port.

esp8266/Makefile

@@ -10,6 +10,7 @@ ifeq ($(ESP_SDK),)
 $(error ESP_SDK must be set)
 endif
 
+PORT = /dev/ttyACM0
 CROSS_COMPILE = xtensa-lx106-elf-
 
 INC =  -I.
@@ -72,9 +73,9 @@ all: $(BUILD)/firmware-combined.bin
 
 deploy: $(BUILD)/firmware-combined.bin
 	$(ECHO) "Writing $< to the board"
-	$(Q)esptool.py --port /dev/ttyACM0 write_flash 0 $<
-	#$(Q)esptool.py --port /dev/ttyACM0 write_flash 0 $(BUILD)/firmware.elf-0x00000.bin
-	#$(Q)esptool.py --port /dev/ttyACM0 write_flash 0x10000 $(BUILD)/firmware.elf-0x10000.bin
+	$(Q)esptool.py --port $(PORT) write_flash 0 $<
+	#$(Q)esptool.py --port $(PORT) write_flash 0 $(BUILD)/firmware.elf-0x00000.bin
+	#$(Q)esptool.py --port $(PORT) write_flash 0x10000 $(BUILD)/firmware.elf-0x10000.bin
 
 $(BUILD)/firmware-combined.bin: $(BUILD)/firmware.elf
 	$(ECHO) "Create $@"