drm/i915/gt: Apply RCS workarounds to the render class

Treat all render engines to the RCS workarounds, simply to avoid using
engine->id when we are trying to think in terms of classes.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Stuart Summers <stuart.summers@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190705124325.14270-1-chris@chris-wilson.co.uk