- Add profiles for bcm2708 subtarget.
- Check subtarget for image generation.

Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@46396 3c298f89-4303-0410-b956-a3cf2f4a3e73