irqchip: mips-gic: Convert remaining shared reg access to new accessors

Convert the remaining accesses to registers in the GIC shared register
block to use the new accessor functions provided by asm/mips-gic.h,
resulting in code which is often shorter & easier to read.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Cc: Jason Cooper <jason@lakedaemon.net>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/17034/


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