MIPS: ralink: Unify SoC id handling

This makes detection a lot easier for audio, wifi, ... drivers.

Signed-off-by: John Crispin <blogic@openwrt.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/11440/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>