IRQCHIP: irq-mips-gic: Extend GIC accessors for 64-bit CMs

Previously, the GIC accessors were only accessing u32 registers but
newer CMs may actually be 64-bit on MIPS64 cores. As a result of which,
extended these accessors to support 64-bit reads and writes.

Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Jason Cooper <jason@lakedaemon.net>
Cc: Andrew Bresticker <abrestic@chromium.org>
Cc: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/10709/


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