ARM: ux500: remove PMU IRQ bouncer

The ux500 PMU IRQ bouncer is getting in the way of some fundametnal
changes to the ARM PMU driver, and it's the only special case that
exists today. Let's remove it.

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>