MIPS: perf: Add proAptiv support

Choose event/cache maps and handle raw event mapping for proAptiv. Update
code comments.

Signed-off-by: Deng-Cheng Zhu <dengcheng.zhu@imgtec.com>
Reviewed-by: Markos Chandras <Markos.Chandras@imgtec.com>
Reviewed-by: James Hogan <james.hogan@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: Steven.Hill@imgtec.com
Patchwork: https://patchwork.linux-mips.org/patch/6527/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>