Simple starting point for adding selftests for i915_gem_gtt, first
try creating a ppGTT and filling it.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170213171558.20942-27-chris@chris-wilson.co.uk