drm/i915: Remove i915_gem_context_create_gvt()

As we are phasing out using the GEM context for internal clients that
need to manipulate logical context state directly, remove the
constructor for the GVT context. We are not using it for anything other
than default setup and allocation of an i915_ppgtt.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190809182518.20486-1-chris@chris-wilson.co.uk