drm/i915/icl: Split getting the DPLLs to port type specific functions

For clarity factor out the combo PHY and TypeC PHY specific code from
icl_get_dplls() into their own functions.

No functional changes.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190628143635.22066-19-imre.deak@intel.com