Create a block of reserved PFNs in shadow translate mode guests, and

Create a block of reserved PFNs in shadow translate mode guests, and
move the shared info and grant table pfns into that block.  This
allows us to remove the get_gnttablist dom0 op, and simplifies the
domain creation code slightly.  Having the reserved block managed by
Xen may also make it slightly easier to handle the case where the
grant table needs to be extended at run time.

Suggested-by: kaf24
Signed-off-by: Steven Smith, sos22@cam.ac.uk