anv: remove limit of 2Gb max allocation

On systems with 48bits of virtual address space, this limit doesn't apply. And since we started requiring softpin, we can be sure that we definitely can allocate more than that without breaking submission.

Use the heap size instead, which is limited to 2Gb on 32bit systems.

Signed-off-by: Lionel Landwerlin lionel.g.landwerlin@intel.com