KVM: ia64: Prepare some structure and routines for kvm use

Register structures are defined per SDM.
Add three small routines for kernel:
ia64_ttag, ia64_loadrs, ia64_flushrs

Signed-off-by: Xiantao Zhang <xiantao.zhang@intel.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>