[IA64] Fix ptc.ga emulation

[IA64] Fix ptc.ga emulation

cset14829(c42ae7839750) was incomplete.

The region register 0 will be clobbered as follows.

time    pcpu0   pcpu1   pcpu2
 |      vcpu0   vcpu1   idle  // assignment of vcpu
 V
        1.vcpu0 issues ptc.ga
        2.vcpu0 sends IPI to vcpu1(pcpu1)
                3.vcpu1 migrates from pcpu1 to pcpu2
                4.pcpu1 receives IPI of 2 and exec ptc_ga_remote_func()
                5.pcpu1 saves and modifies vrr[0]
                        6.vcpu1(pcpu2) modifies vrr[0]
                7.pcpu1 restores vrr[0]         // vrr[0] of 6 is lost

Windows will crash due to this issue.

Signed-off-by: Kouya Shimura <kouya@jp.fujitsu.com>