perf: Add support for user and kernel event sharing

The ARM PMU counters are limited in number. Even for counting similar
events, the PMU driver allocates a new counter. Hence, counters configured
to count similar events are shared. This was only possible for the kernel
clients, but not for user-space clients. Hence, as an extension to this,
the kernel and the user-space are now able to share the similar events.
The counters can be shared between user-space only clients, kernel only
clients, and among user-space and kernel clients. The kernel and user's
attr->type (hardware/raw) and attr->config should be same for them to
share the same counter.

Change-Id: I4a4b35bde6beaf8f2aef74e683a9804e31807013
Signed-off-by: Raghavendra Rao Ananta <rananta@codeaurora.org>