[media] hdmi: rename HDMI_AUDIO_CODING_TYPE_EXT_STREAM to _EXT_CT

As per the suggestion of Thierry Reding rename
HDMI_AUDIO_CODING_TYPE_EXT_STREAM to HDMI_AUDIO_CODING_TYPE_EXT_CT to
be consistent with the CEA-861 spec.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>