spmi: pmic-arb: fix missing interrupts

irq_enable which is called when the device resumes. Note that the
irq_enable is called regardless of whether the interrupt was
marked enabled/disabled in the descriptor or whether it was
masked/unmaked at the controller while resuming.

The current driver unconditionally clears the interrupt in its
irq_enable callback. This is dangerous as any interrupts that
happen right before the resume could be missed.

Remove the irq_enable callback and use mask/unmask instead.

Change-Id: I58695ae0c4905a699003d35498dc36c2a947f3f0
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>