Code restructure in order to simplify class hierarchy
  - remove S390SCLPDevice abstract base class
    and move function pointers into new SCLPEventFacilityClass
  - implement SCLPEventFacility as SysBusDevice
  - use define constants for instance creation strings

The following ascii-art shows the class structure wrt the SCLP EventFacility
before (CURRENT) and after the restructure (NEW):

----
CURRENT:

   "s390-sclp-events-bus"
   +-------------------------+
   |      SCLPEventsBus      |
   |-------------------------|
   |BusState qbus            |
   +-------------------------+

   +-------------------------+
   |   SCLPEventFacility     |  - to be replaced by new SCLPEventFacility,
   |-------------------------|    which will be a SysBusDevice
   |SCLPEventsBus sbus       |
   |DeviceState *qdev        |
   |unsigned int receive_mask|
   +-------------------------+

   +-------------------------+
   |   S390SCLPDeviceClass   |  - to be replaced by new SCLPEventFacilityClass
   |-------------------------|
   |DeviceClass qdev         |
   |*(init)()                |
   +-------------------------+

   "s390-sclp-event-facility"
             |
         instance-of
             |
             V
   "s390-sclp-device"           - this is an abstract class
   +-------------------------+
   |     S390SCLPDevice   (A)|  - to be replaced by new SCLPEventFacility
   |-------------------------|
   |SysBusDevice busdev      |
   |SCLPEventFacility *ef    |
   |                         |
   |*(sclp_command_handler)()|  - these 2 go to new SCLPEventFacilityClass
   |*(event_pending)()       |
   +-------------------------+

----
NEW:

   "s390-sclp-events-bus"
   +-------------------------+
   |      SCLPEventsBus      |
   |-------------------------|
   |BusState qbus            |
   +-------------------------+

   +-------------------------+
   | SCLPEventFacilityClass  |
   |-------------------------|
   |DeviceClass parent_class |
   |                         |
   |*(init)()                |
   |*(command_handler)()     |
   |*(event_pending)()       |
   +-------------------------+

   "s390-sclp-event-facility"
   +-------------------------+
   |   SCLPEventFacility     |
   |-------------------------|
   |SysBusDevice parent_class|
   |SCLPEventsBus sbus       |
   |unsigned int receive_mask|
   +-------------------------+
Signed-off-by: NHeinz Graalfs <graalfs@linux.vnet.ibm.com>
Reviewed-by: NCornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: NChristian Borntraeger <borntraeger@de.ibm.com>