intel-gpu-overlay: Consolidate perf PMU access to library

Various tool modules implement their owm PMU open wrapper which
can be replaced by calling the library one.

v2:
 * Remove extra newline. (Chris Wilson)
 * Commit msg.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>