MIPS: BCM47XX: Add new file for device specific workarounds

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Cc: linux-mips@linux-mips.org
Cc: Hauke Mehrtens <hauke@hauke-m.de>
Patchwork: https://patchwork.linux-mips.org/patch/6627/


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