iommu: msm: Only allow supported perf. events

Only allow supported Performance Monitor Unit (PMU) events to be
selected by users when enabling performance monitoring. This ensures
a more user friendly user interface. Instead of users being allowed to
configure the PMU counters to count events and not seeing the counters
actually work, the PMU interface will now reject setting of counter events
that are not supported.

Change-Id: I5a515d3f3e24c5c66434847925dd92fb49110148
Signed-off-by: Olav Haugan <ohaugan@codeaurora.org>