Before we unpin the buffer used for OA reports and return it to the
system, we need to be sure that the HW has finished writing into it.
For lack of a better idea, poll OACONTROL to check it is switched off.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=106379Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Cc: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: NLionel Landwerlin <lionel.g.landwerlin@intel.com>
Tested-by: NLionel Landwerlin <lionel.g.landwerlin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180511135207.12880-1-chris@chris-wilson.co.uk