irqchip: gic-v3: Refactor gic_enable_redist to support both enabling and disabling

Currently gic_enable_redist configures the redistributors to never
assert WakeRequest signal. However when powering down the processors
with wake-up enabled(i.e suspend), we need to configure it to assert
that signal.

This patch extends gic_enable_redist so that the redistributor can be
configure to assert WakeRequest and hold interrupts as pending. This is
useful in suspending the processors.

This patch also adds check to make sure GICR_WAKER is accessible when
configuring it.

Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
[maz: removed reference to GICD_CTLR.DS and added read-back of
      GICR_WAKER to check that it is not RAZ/WI]
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Link: https://lkml.kernel.org/r/1409065415-20176-2-git-send-email-sudeep.holla@arm.com


Signed-off-by: Jason Cooper <jason@lakedaemon.net>