irqchip: mips-gic: Simplify shared interrupt pending/mask reads

Simplify the reads of the bitmaps indicating pending & masked interrupts
in gic_handle_shared_int() using the __ioread32_copy() &
__ioread64_copy() helper functions.

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/17026/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>