pc-bios/s390-ccw: add some utility code

pc-bios/s390-ccw: add some utility code

IPL_assert(term,message) is introduced to handle error conditions.
ebcdic_to_ascii() to convert chars (mostly to print VOLSERs).
read_block() provision for unified block-number handling.

Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Eugene (jno) Dvurechenski <jno@linux.vnet.ibm.com>
Reviewed-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Jens Freimann <jfrei@linux.vnet.ibm.com>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>