drm/arc: do not rely on drmP.h from drm_gem_cma_helper.h

drmP.h was the only header file in the past and a lot
of files rely on that drmP.h defines everything.
The goal is to one day to delete drmP.h and
as a step towards this it will no longer be included in the
headers files in include/drm/

To prepare arc/ for this add dependencies that
othwewise was pulled in by drmP.h from drm_gem_cma_helper.h

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Noralf Trønnes <noralf@tronnes.org>
Cc: Alexey Brodkin <abrodkin@synopsys.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: David Airlie <airlied@linux.ie>
[danvet: Fix typo in commit message.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20190108192939.15255-10-sam@ravnborg.org