The PMU register are accessed in a non atomic way and they could be
accessed by different threads simultaneously, which could cause
problems this patch adds locking around the PMU registers. In
addition we now also wait till the PMU is actually deactivated.

[ralf@linux-mips.org: Fix spelling mistake in commit message as noticed
by Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>.]
Signed-off-by: NHauke Mehrtens <hauke.mehrtens@lantiq.com>
Acked-by: NJohn Crispin <blogic@openwrt.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/11381/
Patchwork: https://patchwork.linux-mips.org/patch/11396/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>