pc-bios/s390-ccw: add utility functions and "export" some others

Add several utility functions, make IPL_check and IPL_assert generally
available, etc.

Acked-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Eugene (jno) Dvurechenski <jno@linux.vnet.ibm.com>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>