MIPS: Add new option for unique RI/XI exceptions

MIPSr5 added support for unique exception codes for the Read-Inhibit
and Execute-Inhibit exceptions.

Signed-off-by: Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>
Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/7338/


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