KVM: ia64: Implement a uniform vps interface

An uniform entry kvm_vps_entry is added for
vps_sync_write/read, vps_resume_handler/guest,
and branches to differnt PAL service according to the offset.

Singed-off-by: Anthony Xu <anthony.xu@intel.com>
Signed-off-by: Xiantao Zhang <xiantao.zhang@intel.com>
Signed-off-by: Avi Kivity <avi@redhat.com>