s390/kvm: do not rely on the ILC on kvm host protection fauls

commit c0e7bb38c07cbd8269549ee0a0566021a3c729de upstream.

For most cases a protection exception in the host (e.g. copy
on write or dirty tracking) on the sie instruction will indicate
an instruction length of 4. Turns out that there are some corner
cases (e.g. runtime instrumentation) where this is not necessarily
true and the ILC is unpredictable.

Let's replace our 4 byte rewind_pad with 3 byte nops to prepare for
all possible ILCs.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>