KVM: PPC: Book3S HV: Disable page merging in H_SVM_INIT_START

Page-merging of pages in memory-slots associated with a Secure VM
is disabled in H_SVM_PAGE_IN handler.

This operation should have been done the much earlier; the moment the VM
is initiated for secure-transition. Delaying this operation increases
the probability for those pages to acquire new references, making it
impossible to migrate those pages in H_SVM_PAGE_IN handler.

Disable page-migration in H_SVM_INIT_START handling.

Reviewed-by: Bharata B Rao <bharata@linux.ibm.com>
Signed-off-by: Ram Pai <linuxram@us.ibm.com>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>