drm/i915/display/dsi: Add support to pipe D

Adding pipe D support to DSI transcoder.
Not adding it for EDP transcoder code paths as only TGL has 4 pipes
and it do not have a EDP transcoder.

Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191107214559.77087-2-jose.souza@intel.com