[IA64] Make P2M semantics match x86

[IA64] Make P2M semantics match x86

So far the ia64 p2m has the semantic similar to
(the x86 p2m) + (page reference count).
But the differece from the x86 p2m have caused the breakage and work around.
This patch make the ia64 p2m semantic same as x86 to solve it.
- get_page() only for grant table page mapping and foreign domain page
  mapping.
- put_page() only for those pages.
- guest_physmap_remove_page() doesn't touch PGC_allocated bit.

Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>