drm/i915: Move the renderstate setup under gt/

The render state is used to initialise the default RCS context, and only
used during early setup from within the gt code. As such, it makes a
good candidate for placing within gt/, even if it is not yet entirely
clean of our GEM heritage.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190704091925.7391-1-chris@chris-wilson.co.uk