drm/i915: Store mask of enabled infoframes in the crtc state

Store the mask of enabled infoframes in the crtc state. We'll start
with just the readout for HDMI encoder, and we'll expand this
to compute the bitmask in .compute_config() later. SDVO will also
follow later.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20190225174106.2163-4-ville.syrjala@linux.intel.com