MIPS: ath25: add SoC type detection

Detect SoC type based on device ID and board configuration data.

Signed-off-by: Sergey Ryazanov <ryazanov.s.a@gmail.com>
Cc: Linux MIPS <linux-mips@linux-mips.org>
Patchwork: https://patchwork.linux-mips.org/patch/8244/


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