drm/i915: Add new vGPU cap info bit VGT_CAPS_HUGE_GTT

This adds a new vGPU cap info bit VGT_CAPS_HUGE_GTT, which is to detect
whether the host supports shadowing of huge gtt pages. If host does
support it, remove the page sizes restriction for vGPU.

Signed-off-by: Changbin Du <changbin.du@intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1525770425-5373-1-git-send-email-changbin.du@intel.com