drm/i915/dg1: Add DPLL macros for DG1

DG1 has 4 DPLLs where DPLL0 and DPLL1 drive DDIA/B and
DPLL2 and DPLL3 drive DDI-TC1/DDI-TC2.

Introduce DG1_DPLL_CFCRx() helper macros to configure
DPLL registers.

Bspec: 50288, 50299

Cc: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Aditya Swarup <aditya.swarup@intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201014191937.1266226-4-lucas.demarchi@intel.com