anv: Make anv_vma_alloc/free a lot dumber

anv: Make anv_vma_alloc/free a lot dumber

All they do now is take a size, align, and flags and figure out which
heap to allocate in.  All of the actual code to deal with the BO is in
anv_allocator.c.  We want to leave anv_vma_alloc/free in anv_device.c
because it deals with API-exposed heaps so it still makes sense to have
it there.

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3519>