anv/descriptor_set: Ensure that bindings are always in increasing order

Since applications are allowed to specify some set of bindings which need
not be dense they also need not be in order.  For most things, this doesn't
matter, but it could result getting the wrong dynamic offsets. This adds a
quick-and-dirty sort to ensure that everything is always in increasing
order of binding index.

Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
Cc: "12.0" <mesa-stable@lists.freedesktop.org>