Perf: arm64: add perf trace user

perf trace user provides a debugfs node to which a marker string
can be written by userspace. This will create an ftrace and perf
entry containing the current value of L1 and L2 enabled
performance counters and the marker string. This allows usermode
programs to write snapshot entries at specific places in their
code, then see the difference in performance counter values
between those locations.

Change-Id: Ib6f6c6e7333f58fd98c4c0b6ed3d3bbf84a8f830
Signed-off-by: Neil Leeder <nleeder@codeaurora.org>