MIPS: ralink: cleanup the soc specific pinmux data

Before we had a pinctrl driver we used a custom OF api. This patch converts the
soc specific pinmux data to a new set of structs. We also add some new pinmux
setings.

Signed-off-by: John Crispin <blogic@openwrt.org>
Patchwork: http://patchwork.linux-mips.org/patch/8009/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>