s390x/kvm: software breakpoint support

s390x/kvm: software breakpoint support

This patch allows to insert and remove sw breakpoints using the QEMU gdbserver
on s390 as well as to interrupt execution on a breakpoint hit when running
with KVM enabled.

Whenever a software breakpoint is inserted, common code calls kvm ioctl
KVM_UPDATE_GUEST_DEBUG. As this method's default on s390 is to return an error
if not implement, the insertion will fail. Therefore, KVM also has to be
updated in order to make use of software breakpoints.

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>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>