VT'd on Broxton and on Braswell require serialisation of GGTT updates.
However, it seems to only be required for insertion, so drop the
complication and heavyweight stop_machine() for clears. The range will
be serialised again before use.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200130092239.1743672-1-chris@chris-wilson.co.uk