KVM: PPC: Book3S HV: Support reset of secure guest

KVM: PPC: Book3S HV: Support reset of secure guest

Add support for reset of secure guest via a new ioctl KVM_PPC_SVM_OFF.
This ioctl will be issued by QEMU during reset and includes the
the following steps:

- Release all device pages of the secure guest.
- Ask UV to terminate the guest via UV_SVM_TERMINATE ucall
- Unpin the VPA pages so that they can be migrated back to secure
  side when guest becomes secure again. This is required because
  pinned pages can't be migrated.
- Reinit the partition scoped page tables

After these steps, guest is ready to issue UV_ESM call once again
to switch to secure mode.

Signed-off-by: Bharata B Rao <[email protected]>
Signed-off-by: Sukadev Bhattiprolu <[email protected]>
	[Implementation of uv_svm_terminate() and its call from
	guest shutdown path]
Signed-off-by: Ram Pai <[email protected]>
	[Unpinning of VPA pages]
Signed-off-by: Paul Mackerras <[email protected]>