drm/i915: fixup infoframe support for sdvo

At least the worst offenders:
- SDVO specifies that the encoder should compute the ecc. Testing also
  shows that we must not send the ecc field, so copy the dip_infoframe
  struct to a temporay place and avoid the ecc field. This way the avi
  infoframe is exactly 17 bytes long, which agrees with what the spec
  mandates as a minimal storage capacity (with the ecc field it would
  be 18 bytes).
- Only 17 when sending the avi infoframe. The SDVO spec explicitly
  says that sending more data than what the device announces results
  in undefined behaviour.
- Add __attribute__((packed)) to the avi and spd infoframes, for
  otherwise they're wrongly aligned. Noticed because the avi infoframe
  ended up being 18 bytes large instead of 17. We haven't noticed this
  yet because we don't use the uint16_t fields yet (which are the only
  ones that would be wrongly aligned).

This regression has been introduce by

3c17fe4b is the first bad commit
commit 3c17fe4b
Author: David Härdeman <david@hardeman.nu>
Date:   Fri Sep 24 21:44:32 2010 +0200

    i915: enable AVI infoframe for intel_hdmi.c [v4]

Patch tested on my g33 with a sdvo hdmi adaptor.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=25732


Tested-by: Peter Ross <pross@xvid.org> (G35 SDVO-HDMI)
Reviewed-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>