drm/i915/sdvo: Read out HDMI infoframes

drm/i915/sdvo: Read out HDMI infoframes

Read the HDMI infoframes from the hbuf and unpack them into
the crtc state.

Well, actually just AVI infoframe for now but let's write the
infoframe readout code in a more generic fashion in case we
expand this later.

Note that Daniel was sceptical about the benefit if this and
also concerned about the potential for crappy sdvo encoders not
implementing the hbuf read commands. My (admittedly limited)
experience is that such encoders don't implement even the
get/set hdmi encoding commands and thus would always be treated
as dvi only. Hence I believe this is safe, and also IMO preferable
having quirks to deal with missing readout support. The readout
support is neatly isolated in the sdvo code whereas the quirk
would leak to other parts of the driver (state checker, fastboot,
etc.) thus complicating the lives of other people.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20190225174106.2163-8-ville.syrjala@linux.intel.com