drm/i915/dg1: map/unmap pll clocks

DG1 uses 2 registers for the ddi clock mapping, with PHY A and B using
DPCLKA_CFGCR0 and PHY C and D using DPCLKA1_CFGCR0. Hide this behind a
single macro that chooses the correct register according to the phy
being accessed, use the correct bitfields for each pll/phy and implement
separate functions for DG1 since it doesn't share much with ICL/TGL
anymore.

The previous values were correct for PHY A and B since they were using
the same register as before and the bitfields were matching.

v2: Add comment and try to simplify DG1_DPCLKA* macros by reusing
previous ones
v3:
  - Fix DG1_DPCLKA_CFGCR0_DDI_CLK_SEL_MASK() after wrong macro reuse
  - Move phy -> id map to a separate macro (Aditya)
  - Remove DG1_DPCLKA_CFGCR0_DDI_CLK_SEL_MASK where not required
    (Aditya)
  - Use drm_WARN_ON

Cc: José Roberto de Souza <jose.souza@intel.com>
Cc: Clinton Taylor <Clinton.A.Taylor@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Aditya Swarup <aditya.swarup@intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Aditya Swarup <aditya.swarup@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201106210006.837953-1-lucas.demarchi@intel.com