drm/i915/ehl: Implement W/A 22010492432

drm/i915/ehl: Implement W/A 22010492432

As per W/A implemented for TGL to program half of the nominal
DCO divider fraction value which is also applicable on EHL.

Changes since V2:
	- Apply stepping B0 till FOREVER
	- B0 - revid update as per Bspec 29153
Changes since V1:
        - ehl_ used as to keep earliest platform prefix
        - WA required B0 stepping onwards

Cc: Deak Imre <imre.deak@intel.com>
Signed-off-by: Tejas Upadhyay <tejaskumarx.surendrakumar.upadhyay@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201104050655.171185-1-tejaskumarx.surendrakumar.upadhyay@intel.com