drm/i915: Program DFR enable/disable as a GT workaround

DFR programming (which we enable as an optimization on gen11, but must
ensure is disabled on gen12) should be handled as a GT workaround rather
than clock gating initialization.  This will ensure that the programming
of these registers is verified with our typical workaround checks.

Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210717051426.4120328-4-matthew.d.roper@intel.com