drm/i915: Move WaDisableDopClockGating:skl to skl_init_clock_gating()

drm/i915: Move WaDisableDopClockGating:skl to skl_init_clock_gating()

It's silly to have if(SKL) checks in gen9_init_clock_gating() when
we can just move those bits into skl_init_clock_gating().

I'm not entirely convinced we even need this w/a, or if we do
then maybe we want it for kbl/cfl as well. IIRC it was only
listed in the wadb, but that is now dead so can't double check
anymore. Bspec doesn't seem to have any purely skl specific
DOP clock gating workarounds listed.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200716190426.17047-1-ville.syrjala@linux.intel.com
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>