ramips: add kernel support for the Tenda 3G300M

Ralink RT3052F, 4MB flash, 32MB ram, one USB 2.0, two buttons
and seven leds.

Factory image should be used to flash from original firmware.

Signed-off-by: Cezary Jackiewicz <cezary.jackiewicz@gmail.com>
Signed-off-by: Gabor Juhos <juhosg@openwrt.org>

SVN-Revision: 35244