MIPS: BCM63XX: Introduce bcm_readq & bcm_writeq.

Needed for upcoming 6368 CPU support.

[ralf@linux-mips.org: Changed function names as per Sergei's comments.]

Signed-off-by: Maxime Bizon <mbizon@freebox.fr>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/2896/


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