edid: Add an edid_dtd_to_fbmode() helper function

Various u-boot video drivers use fb_videomode structs to store timing info,
add a helper function to convert an EDID detailed timing into a fb_videomode
struct.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
edid: Add an edid_check_checksum() helper function

Add a helper function to check the checksum of an EDID data block.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
sunxi: display: Add DCC & EDID support

Add DCC & EDID support and use it to automatically select the native mode of
the attached monitor. This can be overriden through the hdmi_mode env.
variable.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>