s390/zcrypt: Make ap init functions static.

The ap init functions ap_module_init and ap_debug_init are
only used within ap_bus.c. Make these functions static and
do not declare them in any header file any more.

Signed-off-by: Harald Freudenberger <freude@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>