vk/aub: Use the data directly from the execbuf2

vk/aub: Use the data directly from the execbuf2

Previously, we were crawling through the anv_cmd_buffer datastructure to
pull out batch buffers and things.  This meant that every time something in
anv_cmd_buffer changed, we broke aub dumping.  However, aub dumping should
just dump the stuff the kernel knows about so we really don't need to be
crawling driver internals.