drm/i915/dg1: Add and setup DPLLs for DG1

Add entries for dg1 plls and setup dg1_pll_mgr to reuse ICL callbacks.
Initial setup for shared dplls DPLL0/1 for DDIA/DDIB and DPLL2/3 for
DDI-TC1/DDI-TC2. Configure dpll cfgcrx registers to drive the plls on
DG1.

v2 (Lucas): Reword commit message and add missing update_ref_clks hook
   (requested by Matt Roper)

Signed-off-by: Aditya Swarup <aditya.swarup@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201014191937.1266226-5-lucas.demarchi@intel.com