perf: Fix mutex call with interrupt disabled in cpu_pmu_notify

As cpu_pmu_notify is called in the secondary kernel start API,
the interrupt is still not enabled when cpu_pmu_notify is called.
platform_get_irq uses mutex, it causes a panic - sleeping
function called from invalid context. So use the internal
irq number in arm pmu structure instead of getting it
from platform_get_irq again.

Change-Id: If80b20f13d9c533a0043e5e8eb506611170d11fd
Signed-off-by: Se Wang (Patrick) Oh <sewango@codeaurora.org>