drm/i915: Don't register CRT connector when DDI E can't be used

On HSW/BDW DDI A and E share 2 lanes, so when DDI A requires the
shared lanes DDI E can't be used. The lanes are not supposed to
be dynamically switched between the two uses, so there's no point
in registering the CRT connector when DDI E has no lanes.

v2: Fix typos in the commit message (Paulo)

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1449005396-15319-1-git-send-email-ville.syrjala@linux.intel.com