makefile.iotlab.single.inc.mk: sort IOTLAB_ARCH_ variables definition

Define them in alphabetical order instead on putting the 'iotlab'
specific nodes at first. Prepare for adding new architectures.

dist/testbed-support/makefile.iotlab.single.inc.mk

@@ -65,13 +65,13 @@ _IOTLAB_EXP_ID := $(if $(IOTLAB_EXP_ID),--id $(IOTLAB_EXP_ID))
 IOTLAB_NODE_AUTO_NUM ?= 1
 
 # board-archi mapping
-IOTLAB_ARCHI_iotlab-m3      = m3:at86rf231
+IOTLAB_ARCHI_arduino-zero   = arduino-zero:xbee
+IOTLAB_ARCHI_b-l072z-lrwan1 = st-lrwan1:sx1276
 IOTLAB_ARCHI_iotlab-a8-m3   = a8:at86rf231
+IOTLAB_ARCHI_iotlab-m3      = m3:at86rf231
+IOTLAB_ARCHI_samr21-xpro    = samr21:at86rf233
 IOTLAB_ARCHI_wsn430-v1_3b   = wsn430:cc1101
 IOTLAB_ARCHI_wsn430-v1_4    = wsn430:cc2420
-IOTLAB_ARCHI_samr21-xpro    = samr21:at86rf233
-IOTLAB_ARCHI_arduino-zero   = arduino-zero:xbee
-IOTLAB_ARCHI_b-l072z-lrwan1 = st-lrwan1:sx1276
 IOTLAB_ARCHI := $(IOTLAB_ARCHI_$(BOARD))
 
 # Try detecting the node automatically