ar71xx: build images for the TL-MR11U v2

[juhosg: use different profile name for v1 and v2, and add
multi profile to build for both versions]

Signed-off-by: Guilhem Lettron <guilhem@lettron.fr>
Signed-off-by: Gabor Juhos <juhosg@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@36038 3c298f89-4303-0410-b956-a3cf2f4a3e73