MIPS: BCM47XX: Detect some more Linksys devices

The Linksys WRT54G/GS/GL family uses the same boardtype numbers, and
the same gpio configuration. The boardtype numbers are changing with
the hardware versions, but these hardware numbers are different or each
model.
Detect them all as one device, this also worked in OpenWrt.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Cc: linux-mips@linux-mips.org
Cc: zajec5@gmail.com
Patchwork: https://patchwork.linux-mips.org/patch/6591/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>