s390x: empty function stubs in preparation for __KVM_HAVE_GUEST_DEBUG

s390x: empty function stubs in preparation for __KVM_HAVE_GUEST_DEBUG

This patch creates empty function stubs (used by the gdbserver) in preparation
for the hw debugging support by kvm on s390, which will enable the
__KVM_HAVE_GUEST_DEBUG define in the linux headers and require these methods on
the qemu side.

Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Jens Freimann <jfrei@linux.vnet.ibm.com>
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Cc: qemu-stable@nongnu.org
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>