videomodes: Add video_edid_dtd_to_ctfb_res_modes helper function

Add a video_edid_dtd_to_ctfb_res_modes helper function to convert an EDID
detailed timing to a struct ctfb_res_modes.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Anatolij Gustschin <agust@denx.de>