drivers/video: fsl-diu-fb: store EDID data in the global object

Although the DIU driver creates five framebuffer devices, only the first
one controls the physical display.  The remaining four are virtual "AOIs".
Therefore, the EDID data should be stored in the global fsl_diu_data
object, instead of the per-framebuffer object.

Signed-off-by: Timur Tabi <timur@freescale.com>