Upstreamed: Fix for spurious guest NMI watchdog lockup reports

[paulusmack]

This is to record the fact that hostos-1.0 includes two commits that fix a bug that cause guests to give spurious NMI watchdog reports. The commits are:

2f1956b ("KVM: PPC: Book3S: Treat VTB as a per-subcore register, not per-thread", 2016-09-15)
3d4f21c ("KVM: PPC: Book3S HV: Take out virtual core piggybacking code", 2016-09-15)

These commits are upstream in v4.9-rc1 with commit IDs 88b02cf and b009031.