irqchip/brcmstb-l2: Use _irqsave locking variants in non-interrupt code

commit 33517881 upstream.

Using the irq_gc_lock/irq_gc_unlock functions in the suspend and
resume functions creates the opportunity for a deadlock during
suspend, resume, and shutdown. Using the irq_gc_lock_irqsave/
irq_gc_unlock_irqrestore variants prevents this possible deadlock.

Fixes: 7f646e92

 ("irqchip: brcmstb-l2: Add Broadcom Set Top Box Level-2 interrupt controller")
Signed-off-by: Doug Berger <opendmb@gmail.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
[maz: tidied up $SUBJECT]
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>