irqchip/mips-gic: Use effective affinity to unmask

Commit 7778c4b2 ("irqchip: mips-gic: Use pcpu_masks to avoid reading
GIC_SH_MASK*") adjusted the way we handle masking interrupts to set &
clear the interrupt's bit in each pcpu_mask. This allows us to avoid
needing to read the GIC mask registers and perform a bitwise and of
their values with the pending & pcpu_masks.

Unfortunately this didn't quite work for IPIs, which were mapped to a
particular CPU/VP during initialisation but never set the affinity or
effective_affinity fields of their struct irq_desc. This led to them
losing their affinity when gic_unmask_irq() was called for them, and
they'd all become affine to cpu0.

Fix this by:

 1) Setting the effective affinity of interrupts in
    gic_shared_irq_domain_map(), which is where we actually map an
    interrupt to a CPU/VP. This ensures that the effective affinity mask
    is always valid, not just after explicitly setting affinity.

 2) Using an interrupt's effective affinity when unmasking it, which
    prevents gic_unmask_irq() from unintentionally changing which
    pcpu_mask includes an interrupt.


Fixes: 7778c4b2 ("irqchip: mips-gic: Use pcpu_masks to avoid reading GIC_SH_MASK*")
Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Jason Cooper <jason@lakedaemon.net>
Link: https://lkml.kernel.org/r/20170922062440.23701-3-paul.burton@imgtec.com