perf: arm: fix IRQ initializations in the driver

During the ARM PMU driver's probe, the IRQ number and state
are set when requesting for the IRQ lines. However, these
values are re-initialized when the driver tries to register
with the perf framework later. The bug prevents the driver
from re-enabling the interrupts during the CPU hotplug-on
case (or any IRQ operation thereafter), thus not triggering
any interrupt. Perf sampling events would be mainly impacted
by this as they update the samples for every overflow interrupt.

Hence, moving the initializations of the IRQ number and state
after the arm_pmu structure is allocated. The correct values
can be recorded after requesting the IRQ.

Change-Id: Ia4361a31e9e960efc7156f813c543574b197ff68
Signed-off-by: Raghavendra Rao Ananta <rananta@codeaurora.org>