Revert "drm/i915/display: Drop FIXME about turn off infoframes"

Looks this FIXME is still valid as we need a way to tell LSPCON to
stop sending infoframes, so reverting it.

This reverts commit 3f409e4c.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210610194527.84997-1-jose.souza@intel.com