arm: perf: make of_pmu_irq_cfg take arm_pmu

To support multiple PMUs we'll need to pass the arm_pmu instance around.
Update of_pmu_irq_cfg to take an arm_pmu, and acquire the platform
device from this.

Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>