Makefile.include: include iotlab.single.inc.mk before checking FLASHFILE
Makefile.include: include iotlab.single.inc.mk before checking FLASHFILE

This way FLASHFILE is either already defined by the board and, if not,
the default one for iotlab can be used.

basilfx/RIOT,kaspar030/RIOT,toonst/RIOT,smlng/RIOT,jasonatran/RIOT,yogo1212/RIOT,mtausig/RIOT,OTAkeys/RIOT,OTAkeys/RIOT,basilfx/RIOT,jasonatran/RIOT,yogo1212/RIOT,miri64/RIOT,jasonatran/RIOT,kYc0o/RIOT,RIOT-OS/RIOT,ant9000/RIOT,jasonatran/RIOT,ant9000/RIOT,ant9000/RIOT,OTAkeys/RIOT,miri64/RIOT,aeneby/RIOT,kYc0o/RIOT,x3ro/RIOT,OTAkeys/RIOT,mtausig/RIOT,OlegHahm/RIOT,smlng/RIOT,authmillenon/RIOT,jasonatran/RIOT,smlng/RIOT,miri64/RIOT,kaspar030/RIOT,OlegHahm/RIOT,josephnoir/RIOT,kYc0o/RIOT,mtausig/RIOT,smlng/RIOT,ant9000/RIOT,RIOT-OS/RIOT,kYc0o/RIOT,yogo1212/RIOT,kYc0o/RIOT,smlng/RIOT,OTAkeys/RIOT,RIOT-OS/RIOT,mtausig/RIOT,toonst/RIOT,kaspar030/RIOT,basilfx/RIOT,authmillenon/RIOT,josephnoir/RIOT,x3ro/RIOT,authmillenon/RIOT,authmillenon/RIOT,aeneby/RIOT,basilfx/RIOT,aeneby/RIOT,miri64/RIOT,aeneby/RIOT,aeneby/RIOT,toonst/RIOT,yogo1212/RIOT,OlegHahm/RIOT,yogo1212/RIOT,mtausig/RIOT,RIOT-OS/RIOT,OlegHahm/RIOT,OlegHahm/RIOT,x3ro/RIOT,kaspar030/RIOT,authmillenon/RIOT,toonst/RIOT,toonst/RIOT,ant9000/RIOT,josephnoir/RIOT,josephnoir/RIOT,basilfx/RIOT,RIOT-OS/RIOT,yogo1212/RIOT,kaspar030/RIOT,miri64/RIOT,josephnoir/RIOT,x3ro/RIOT,authmillenon/RIOT,x3ro/RIOT