drm/i915/dg1: Enable ports

For DG1 we have a little of mix up wrt to DDI/port names and indexes.
Bspec refers to the ports as DDIA, DDIB, DDI USBC1 and DDI USBC2
(besides the DDIA, DDIB, DDIC, DDID), but the previous naming is the
most unambiguous one. This means that for any register on Display Engine
we should use the index of A, B, D and E. However in some places this is
not true:

- VBT: uses C and D and have to be mapped to D/E

- IO/Combo: uses C and D, but we already differentiate those when
  we created the phy vs port distinction.

This additional mapping for VBT and phy are already covered in previous
patches, so now we can initialize all the DDIs as A, B, D and E.

v2: Squash previous patch enabling just ports A and B since most of the
pumbling code is already merged now

Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Clinton Taylor <Clinton.A.Taylor@intel.com>
Signed-off-by: Aditya Swarup <aditya.swarup@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201117084836.2318234-1-lucas.demarchi@intel.com