MIPS: traps: Dump the HTW registers on a MC exception

The HTW registers can be useful to debug a MC exception.

Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/8400/


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