MIPS: CM: Add CM GCR_BEV_BASE accessors

MIPS: CM: Add CM GCR_BEV_BASE accessors

Generate accessor functions for the GCR_BEV_BASE register introduced by
CM3, for use by a later patch.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: Matt Redfearn <matt.redfearn@imgtec.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/12331/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>