kernel - VM PAGER part 2/2 - Expand vinitvmio() and vnode_pager_alloc()

kernel - VM PAGER part 2/2 - Expand vinitvmio() and vnode_pager_alloc()

* vinitvmio() is responsible for assigning the initial VM object size based
  on the file size.  Adjust vinitvmio() to conform to the new nvextendbuf()
  and nvtruncbuf() API.

* vinitvmio() has been given two additional parameters, blksize and boff,
  to allow it to determine how much larger the VM object must be relative
  to the byte-granular file size passed to it.

* Remove vm_page_alloc() and remove the pgo_alloc vector from struct
  pagerops.  Convert all the VM pager allocation procedures into global
  procedures which are called directly.  Trying to feed everything through
  a single function was a joke when all the callers knew precisely what
  kind of VM object they were creating anyway.

  Add the extra arguments to vnode_pager_alloc() which vinitvmio() needs
  to pass in.