Makefile: sort list of defconfig targets in make help output

Without sorting this list is completely unreadable for ARCH=arm.
Signed-off-by: Konstantin Khlebnikov <k.khlebnikov@samsung.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>

Makefile

@@ -1232,7 +1232,7 @@ rpm: include/config/kernel.release FORCE
 # ---------------------------------------------------------------------------
 
 boards := $(wildcard $(srctree)/arch/$(SRCARCH)/configs/*_defconfig)
-boards := $(notdir $(boards))
+boards := $(sort $(notdir $(boards)))
 board-dirs := $(dir $(wildcard $(srctree)/arch/$(SRCARCH)/configs/*/*_defconfig))
 board-dirs := $(sort $(notdir $(board-dirs:/=)))