drm/i915/display/icl+: Do not program clockgating

drm/i915/display/icl+: Do not program clockgating

Talked with HW team and this is a left over, driver should not
program clockgating, mg or dekel firmware is reponsible for any
clockgating programing.

Also removing the register and bits definition related to clockgating.

v2:
Added WARN_ON

v3:
Only calling icl_phy_set_clock_gating() on intel_ddi_pre_enable_hdmi
for GEN11

v4:
ICL should also not program clockgating (thanks Matt for catching
this)

BSpec issue: 20885
BSpec: 49292
BSpec: 21735
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200107170922.153612-1-jose.souza@intel.com