s390x: Use interrupts in SCLP and add locking

We need to properly implement interrupt handling for SCLP, because on
z/VM and LPAR SCLP calls are not synchronous!

Also with smp CPUs have to compete for sclp. Let's add some locking,
so they execute sclp calls in an orderly fashion and don't compete for
the data buffer.

Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20190920080356.1948-2-frankja@linux.ibm.com>
Acked-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>