[IA64] domheap: Allocate privregs from domain heap for VTi domain

[IA64] domheap: Allocate privregs from domain heap for VTi domain

- Pin privregs down with both dtr/itr so that privregs can be allocated
  from the domain heap
- Introduce vmx_vpd_pin()/vmx_vpd_unpin().
  The vpd area is pinned down when current.  But two functions,
  update_vhpi() and alloc_vpd() are exceptions.
  We have to pin down the area before PAL call.
- Minor twist context switch not to use unpinned vpd area.
  vmx_load_state() needs the vpd area pinned down.
  Call it after vmx_load_all_rr()
- Fix vmx_load_all_rr()
  vmx_switch_rr7() sets psr.ic = 0 so that clearing psr.ic before calling
  vmx_switch_rr7() doesn't make sense.
- Improve vmx_switch_rr7()
  It sets psr.ic = 0 after switching to physical mode. But it can be
  done at the switching time.

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