drm: Add DRM support for tiny LCD displays

tinydrm provides helpers for very simple displays that can use
CMA backed framebuffers and need flushing on changes.

Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Thierry Reding <treding@nvidia.com>