Perf: core: create/delete shared kernel events

Frequently drivers want to monitor some event like L2 misses
and cycles+instructions. If more than 1 driver wants to monitor
the same event and the event attributes are the same then we
can create just one instance of the event and let drivers
share the event. Add shared event create and delete
routines.

Change-Id: Ided097bdbb832527f4c8c9ab32d361cc1caba1f0
Signed-off-by: Patrick Fay <pfay@codeaurora.org>
Signed-off-by: Raghavendra Rao Ananta <rananta@codeaurora.org>