MIPS: perf: Add perf functionality for BMIPS5000

Add hardware performance counter support to kernel "perf" code for
BMIPS5000. The BMIPS5000 performance counters are similar to MIPS
MTI cores, so the changes were mostly made in perf_event_mipsxx.c
which is typically for MTI cores.

Signed-off-by: Al Cooper <alcooperx@gmail.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/4109/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>