ppc/spapr: Support reboot of secure pseries guest

ppc/spapr: Support reboot of secure pseries guest

A pseries guest can be run as a secure guest on Ultravisor-enabled
POWER platforms. When such a secure guest is reset, we need to
release/reset a few resources both on ultravisor and hypervisor side.
This is achieved by invoking this new ioctl KVM_PPC_SVM_OFF from the
machine reset path.

As part of this ioctl, the secure guest is essentially transitioned
back to normal mode so that it can reboot like a regular guest and
become secure again.

This ioctl has no effect when invoked for a normal guest. If this ioctl
fails for a secure guest, the guest is terminated.

Signed-off-by: Bharata B Rao <bharata@linux.ibm.com>
Message-Id: <20191219031445.8949-3-bharata@linux.ibm.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>