video, sm501: add edid and commandline support

- add commandline options:
  sm501fb.mode:
    Specify resolution as "<xres>x<yres>[-<bpp>][@<refresh>]"
  sm501fb.bpp:
    Specify bit-per-pixel if not specified mode

- Add support for encoding display mode information
  in the device tree using verbatim EDID block.

  If the "edid" entry in the "smi,sm501" node is present,
  the driver will build mode database using EDID data
  and allow setting the display modes from this database.

Signed-off-by: Heiko Schocher <hs@denx.de>
cc: linux-fbdev@vger.kernel.org
cc: devicetree-discuss@ozlabs.org
cc: Ben Dooks <ben@simtec.co.uk>
cc: Vincent Sanders <vince@simtec.co.uk>
cc: Samuel Ortiz <sameo@linux.intel.com>
cc: linux-kernel@vger.kernel.org
cc: Randy Dunlap <rdunlap@xenotime.net>
cc: Paul Mundt <lethal@linux-sh.org>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>