s390/sthyi: Use cached data when diag is busy

When sthyi is being emulated, data from diag204 is used. If diag204
returns busy, previously cached sthyi info block is returned to the
caller and cache expiry is set to expired.

Acked-by: Heiko Carstens <hca@linux.ibm.com>
Reviewed-by: Tobias Huschle <huschle@linux.ibm.com>
Signed-off-by: Tobias Huschle <huschle@linux.ibm.com>
Signed-off-by: Mete Durlu <meted@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>