MIPS: CPS: Set Status.BEV bit during early boot

Set the Status.BEV bit throughout the early startup of a secondary core
such that if an exception occurs the core branches to one of the
exception vector entries from cps-vec.S, rather than branching to
whatever is set in EBase.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: Markos Chandras <markos.chandras@imgtec.com>
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/11200/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>