[include] ensure that profile Makefiles are sourced in alphabetical order

[include] ensure that profile Makefiles are sourced in alphabetical order
Since make 3.82 does not guarantee file ordering anymore, target profiles might
get included in random order, leading to bad default values when only selecting
the toplevel target and populating the .config with defconfig.
This commit should also fix the ar71xx snapshot builds.

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@31449 3c298f89-4303-0410-b956-a3cf2f4a3e73