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

This patch enables the sending of AVI infoframes in
drivers/gpu/drm/i915/intel_hdmi.c.

My receiver currently loses sync when the HDMI output on my computer
(DG45FC motherboard) is switched from 800x600 (the BIOS resolution) to
1920x1080 as part of the boot. Fixable by switching inputs on the receiver
a couple of times.

With this patch, my receiver has not lost sync yet (> 40 tries).

Fourth version, now based on drm-intel-next from:
git://git.kernel.org/pub/scm/linux/kernel/git/ickle/drm-intel.git



Two questions still remain:

I'm assuming that the sdvo hardware also stores a header ECC byte in
the MSB of the first dword - is this correct?

Does the SDVOB and SDVOC handling in intel_hdmi_set_avi_infoframe()
look correct?

Signed-off-by: David Härdeman <david@hardeman.nu>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>