Add mmp display subsystem to support Marvell MMP display controllers.

This subsystem contains 4 parts:
--fb folder
--core.c
--hw folder
--panel folder

1. fb folder contains implementation of fb.  fb get path and overlay
   from common interface and operates on these structures.

2. core.c provides common interface for a hardware abstraction.  Major
   parts of this interface are:

   a) Path: path is a output device connected to a panel or HDMI TV.  Main
      operations of the path is set/get timing/output color.  fb operates
      output device through path structure.

   b) Ovly: Ovly is a buffer shown on the path.

      Ovly describes frame buffer and its source/destination size, offset,
      input color, buffer address, z-order, and so on.  Each fb device maps
      to one overlay.

3. hw folder contains implementation of hardware operations defined by
   core.c.  It registers paths for fb use.

4. panel folder contains implementation of panels.  It's connected to
   path.  Panel drivers would also regiester panels and linked to path
   when probe.
Signed-off-by: NZhou Zhu <zzhu3@marvell.com>
Signed-off-by: NLisa Du <cldu@marvell.com>
Cc: Guoqing Li <ligq@marvell.com>
Acked-by: NHaojian Zhuang <haojian.zhuang@gmail.com>
Cc: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>