drm/i915/icl: Get pipe timings for DSI

Transcoder timings for Gen11 DSI encoder
is available at pipe level unlike in older platform
where port specific registers need to be accessed.

v2 by Jani:
 - get timings for (!dsi || icl) instead of (dsi && icl).

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/f60e0c1aee08248e758da3219d3239898b43ba41.1543500286.git.jani.nikula@intel.com