There is currently conflicting documentation on which steppings the
workaround is needed, up to C vs. forever. However there is post-C
stepping hardware that doesn't report port presence on DDI A, leading to
black screen on eDP. Assume the strap isn't connected, and try to enable
DDI A on these machines. (We'll still check the VBT for the info in DDI
init.)

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Mika Westerberg <mika.westerberg@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>