s390/sclp: release SCLP early buffer after kernel initialization

The SCLP early buffer is used only during kernel initialization and can be
freed afterwards. The only way to ensure that it is not released while
being in use, is to release it in free_initmem().

Acked-by: Heiko Carstens <hca@linux.ibm.com>
Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Alexander Egorenkov <egorenar@linux.ibm.com>
[agordeev@linux.ibm.com: added debug output]
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>