video: Add i.MX23/28 framebuffer driver

changes since v2:

- use v3 and v4 for specifying the ip version instead of i.MX23/28.
  This is a better namespace when future versions are added.
- rename mach/fb.h to mach/mxsfb.h

changes since v1:
- Add a LCDC_ prefix to the register names.
- use set/clear registers where appropriate
- protect call to mxsfb_disable_controller() in mxsfb_remove()
  with a (host->enabled) as suggested by Lothar Wassmann

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Acked-by: Shawn Guo <shawn.guo@freescale.com>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: linux-fbdev@vger.kernel.org