lib: s390x: Print PGM code as hex

We have them defined as hex constants in lib/s390x/asm/arch_def.h so
why not print them as hex values?

Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>