drm/i915: Restore DP-E to VBT mapping table

We accidentally dropped matching for DVO_PORT_DPE from the VBT mapping
table when we refactored the function.  Restore it.

Fixes: 4628142a

 ("drm/i915/rkl: provide port/phy mapping for vbt")
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20200606031803.3309624-1-matthew.d.roper@intel.com