drm/i915/tgl: Add dkl phy pll calculations

Extending ICL mg calculations to also support dkl calculations.

v3:
Fixing iref_trim calculation for 38400 refclock

BSpec: 49204

Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Vandita Kulkarni <vandita.kulkarni@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190924210040.142075-5-jose.souza@intel.com