drm: add DRM_MODE_FLAG_DBLCLK to CEA modes requiring it

CEA modes 6, 7, 8, 9, 21, 22, 23, 24, 44, 45, 50, 51, 54, 55, 58 and 59
require sending pixel data 2 times. This doesn't mean the modes will
work yet, but now the drivers know they're different.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>