Algorithm - version 2

Decouple allocator algorithm from virtual memory management.

struct uvm_addr_functions {
  int  (*uaddr_select) (map, state, addr_out, entry_out,
        sz, align, offset, prot, hint);
  void (*uaddr_free_insert) (map, state, entry);
  void (*uaddr_free_remove) (map, state, entry);
  void (*uaddr_destroy) (state);
};

struct uvm_addr_state {
  vaddr_t                    uaddr_minaddr;
  vaddr_t                    uaddr_maxaddr;
  struct uvm_addr_functions *uaddr_functions;
};