ar71xx: add support for TP-Link TL-MR11U

ar71xx: add support for TP-Link TL-MR11U

Adds support for TL-MR11U, a portable router with very similar
hardware to the TL-WR703N and TL-MR3020, but with an onboard
2000mAh battery.

Tested, working:
All interfaces (Ethernet, 802.11n, USB)
WPS & Reset switches (Power appears to be a hardware slider)
Ethernet, Wifi, 3G LEDs (Power & charging LEDs hardware controlled)
Sysupgrade

[juhosg: fix indentations to use TABs instead of spaces, fix 3.2 patch
breakage]

Signed-off-by: Simon Taylor <simon.taylor.uk@gmail.com>
SVN-Revision: 29972