drm/radeon/cayman: setup hdp to invalidate and flush when asked

On cayman we need to set the bit to cause HDP flushes to invalidate the
HDP cache also.

Reviewed-by: Alex Deucher <alexdeucher@gmail.com>
cc: stable@kernel.org
Signed-off-by: Dave Airlie <airlied@redhat.com>

diff --cc drivers/gpu/drm/radeon/ni.c
Simple merge

diff --cc drivers/gpu/drm/radeon/nid.h
Simple merge