s390/sclp: add open for business support

Provide a user space interface and an enhancement to the sclp device driver
which allows to send an 'Open for Business' event from the operating system
to the Support Element. The 'Open for Business' event is used to signal the
Support Element that the operating system (or an application running on top
of it) is up and running.

Signed-off-by: Jochen Schweflinghaus <schwefel@de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>