drm/edid: Increase size of VDB and CMDB bitmaps to 256 bits

CEA-861-G adds modes up to 219, so increase the size of the
maps in preparation for adding the new modes to drm_edid.c.

Signed-off-by: Thomas Anderson <thomasanderson@google.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191210221048.83628-1-thomasanderson@google.com