drm/i915/tgl: init ddi port A-C for Tiger Lake

This patch initializes DDI PORT A, B & C for Tiger lake. Other
TC ports need to be initialized later once corresponding code is there.

Cc: Madhav Chauhan <madhav.chauhan@intel.com>
Signed-off-by: Mahesh Kumar <mahesh1.kumar@intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190711173115.28296-15-lucas.demarchi@intel.com