vulkan/wsi: Move get_images into common code

vulkan/wsi: Move get_images into common code

This moves bits out of all four corners (anv, radv, x11, wayland) and
into the wsi common code.  We also switch to using an outarray to ensure
we get our return code right.

Reviewed-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Chad Versace <chadversary@chromium.org>