Perf: Add support for L2 cycle counter in default list

Adding the L2 cycle counter in the default list of events
has the advantage that the user can do a :

perf stat -e l2-cycles -e cycles ls

and see the outputs for the L2 cycle counter and L1 cycle
counter separately. Previously, it was only accessible via
the raw code "rsfe".

This method also allows us to program the L2 cycle counter
only from one CPU.

The changes in this patch are used by the userspace perf
tool.

Change-Id: I61b85b48f5474fe9f6ffb1a405b60b4332ab60c7
Signed-off-by: Ashwin Chaugule <ashwinc@codeaurora.org>