MIPS: ralink: adds reset code

Resetting these SoCs requires no real magic. The code is straight forward.

Signed-off-by: John Crispin <blogic@openwrt.org>
Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Patchwork: http://patchwork.linux-mips.org/patch/4891/