s390: Make cpc_name accessible

sclp_ocf.c is the only way to get the cpc name, as it registers the
sole event handler for the ocf event. By creating a new global
function that copies that name, we make it accessible to the world
which longs to retrieve it.

Additionally we now also store the cpc name as EBCDIC, so we don't
have to convert it to and from ASCII if it is requested in native
encoding.

Signed-off-by: Janosch Frank <frankja@linux.vnet.ibm.com>
Reviewed-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Acked-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>