hal: Allow to set used PLO_DEVICES from outside

hal/armv7m/stm32/l4/Makefile

@@ -15,9 +15,11 @@ CFLAGS += -mfloat-abi=soft
 PLO_COMMANDS ?= alias app bankswitch call console copy dump echo go help kernelimg map mem mpu \
   phfs reboot script wait
 
-#include devices/pipe-rtt/Makefile
-include devices/uart-stm32l4x6/Makefile
-include devices/flash-stm32/Makefile
-include devices/ram-storage/Makefile
+PLO_ALLDEVICES := uart-stm32l4x6 flash-stm32 ram-storage # pipe-rtt
+PLO_DEVICES ?= $(PLO_ALLDEVICES)
+
+PLO_USED_DEVS = $(filter $(PLO_ALLDEVICES), $(PLO_DEVICES))
+
+include $(foreach dev, $(PLO_USED_DEVS), devices/$(dev)/Makefile)
 
 OBJS += $(addprefix $(PREFIX_O)hal/$(TARGET_SUFF)/stm32/l4/, _init.o stm32l4.o timer.o console.o)