drm/i915: Remove special handling for !RCS_MASK()

With both XEHPSDV and PVC removed (as platforms, most of their code
remain used by others), there's no need to handle !RCS_MASK() as
other platforms don't ever have fused-off render. Remove those code
paths and the special WA flag when initializing GuC.

Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Acked-by: Tvrtko Ursulin <tursulin@ursulin.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20240320060543.4034215-7-lucas.demarchi@intel.com
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>