drm/gma500: mdfld: Reuse video/mipi_display.h

The GMA500 driver redefines many constants already found in the generic
header. Replace uses of the custom defines by the standard ones and get
rid of the duplicate defininitions.

Acked-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>