Perf: Re-enable counters after power collapse

Counters need to be individually re-enabled after the CPU
comes out of power collapse. Without this the counters
will simply be set to their MAX period and starting the PMU
will have no effect.

Change-Id: I3988a45277057eb80cf580b90ce697d0e6a00c43
Signed-off-by: Ashwin Chaugule <ashwinc@codeaurora.org>