staging: drm/omap: add drm_plane support

Because framebuffer layer and overlay scanout video pipes are basically
thing in OMAP display subsystem (the only difference being that the first
video pipe does not support scaling or YUV formats), much of the CRTC
code is pulled into the plane implementation, and a private plane object
is used by the CRTC object.  This avoids code duplication between the
plane and CRTC.

Signed-off-by: Rob Clark <rob@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>