MIPS: Introduce board_cache_error_setup() hook.

This is used in subsequent patches.

Signed-off-by: David Daney <david.daney@cavium.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/3819/


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