firmware-utils/mktplinkfw: add support for the TL-MR10U board

Based on andelf's patch:
http://andelf.diandian.com/post/2013-05-22/40050677370



Signed-off-by: Oleg Titov <oleg.titov@gmail.com>
Patchwork: http://patchwork.openwrt.org/patch/3840/


Signed-off-by: Gabor Juhos <juhosg@openwrt.org>

SVN-Revision: 37549