drm/i915/dg1: Remove SHPD_FILTER_CNT register programming

Bspec asks us to remove the special programming of the
SHPD_FILTER_CNT register which we have been doing since CNP+.

Bspec: 49305

Cc: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200713182321.12390-5-lucas.demarchi@intel.com