This changest allows grant mappings to arbitrary PTEs.

This changest allows grant mappings to arbitrary PTEs.

The map operation now takes PTE addresses as well as virtual
addresses.  The contains_pte flag is used to indicate what sort of
address is in the map request.

Additionally, this patch:

  - fixes grant mappings to user space.
  - fixes overflow testing when you run out of maptrack entry space.

Signed-off-by: Andrew Warfield <andrew.warfield@cl.cam.ac.uk>
Signed-off-by: Leoffrey Lefebvre <geoffrey.g.lefebvre@intel.com>