arm_pmu: Introduce pmu_irq_ops

Currently the PMU interrupt can either be a normal irq or a percpu irq.
Supporting NMI will introduce two cases for each existing one. It becomes
a mess of 'if's when managing the interrupt.

Define sets of callbacks for operations commonly done on the interrupt. The
appropriate set of callbacks is selected at interrupt request time and
simplifies interrupt enabling/disabling and freeing.

Cc: Julien Thierry <julien.thierry.kdev@gmail.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Julien Thierry <julien.thierry@arm.com>
Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>