expose control over unpriv perf access to shell

(cherry picked from commit af45d3c9ddbae3e810ec269a0ef4f6ec1886888c)

This allows the shell user to control whether unprivileged access to
perf events is allowed.

To enable unprivileged access to perf:

    adb shell setprop security.perf_harden 0

To disable it again:

    adb shell setprop security.perf_harden 1

This allows Android to disable this kernel attack surface by default,
while still allowing profiling tools to work automatically. It can also
be manually toggled, but most developers won't ever need to do that if
tools end up incorporating this.

Bug: 29054680

Change-Id: Idcf6a2f6cbb35b405587deced7da1f6749b16a5f
1 file changed