compositor-drm: Use plane_state_coords_for_view for cursor

Use the new helper to populate the cursor state as well, with some
special-case handling to account for how we always upload a full-size
BO.

As this now fully takes care of buffer transformations, HiDPI client
cursors work, and we also clip the cursor plane completely to CRTC
bounds.

Signed-off-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reported-by: Derek Foreman <derekf@osg.samsung.com>
Tested-by: Emre Ucan <eucan@de.adit-jv.com>
Fixes: https://gitlab.freedesktop.org/wayland/weston/issues/118