drm/i915/icl: Define TRANS_CONF register for DSI

This patch defines TRANS_CONF registers for DSI ports
0 and 1. Bitfields of these registers used for enabling
and reading the current state of transcoder.

v2: Add blank line before comment

v3 by Jani:
 - Move DSI specific .pipe_offsets to GEN11_FEATURES
 - Macro placement and comment juggling

Signed-off-by: Madhav Chauhan <madhav.chauhan@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/3aa11e41ea0d4eb434423cc5ddf0a63b19d54deb.1539613303.git.jani.nikula@intel.com