[media] adv7604: Replace prim_mode by mode

Changes the way the primary mode is handled:
- Remove it from platform_data since it doesn't belong there.
- Add a new mode enum for use with s_routing.
- Collapse the two HDMI modes into one HDMI mode: when setting up the
  timings manually we do not need to select HDMI_COMP mode. That's only
  needed when selecting a preset.
This patch prepares for the next step where we switch to using the presets
where available.

Signed-off-by: Mats Randgaard <mats.randgaard@cisco.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>