Perf: Add PMU names to perf output

Output of raw events in perf tools can be hard to distinguish
when multiple PMU's have the same event encoding.

Show the PMU name along with the counter output.

e.g.

 Performance counter stats for 'ls':

          4514688 msm-l2 0x1

Change-Id: I65d4ac03c2fd562519ab78524b37467e7d53dbb3
Signed-off-by: Ashwin Chaugule <ashwinc@codeaurora.org>