drm/i915: Mark up vGPU support for full-ppgtt

For compatibility reasons, we only care if the vGPU host provides
support for full-ppgtt. This is independent of the addressable memory
size, so remove the conflation of 48b from the capability name.

Based on a patch by Bob Paauwe.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Bob Paauwe <bob.j.paauwe@intel.com>
Cc: Zhenyu Wang <zhenyuw@linux.intel.com>
Cc: Zhi Wang <zhi.a.wang@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190314223839.28258-1-chris@chris-wilson.co.uk