drm/i915/icl: push pll to port mapping/unmapping to ddi encoder hooks

drm/i915/icl: push pll to port mapping/unmapping to ddi encoder hooks

Unclutter the haswell_crtc_enable() and haswell_crtc_disable() functions
a bit by moving the pll to port mapping and unmapping functions to the
ddi encoder hooks. This allows removal of a bunch of boilerplate code
from the functions.

Additionally, the ICL DSI encoder needs to do the clock gating and
ungating slightly differently, and this allows its own handling in a
clean fashion.

Cc: Madhav Chauhan <madhav.chauhan@intel.com>
Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Madhav Chauhan <madhav.chauhan@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/f8e2982ceea4c05dc254a0c15e2b3be1d5f271d3.1543500285.git.jani.nikula@intel.com