s390/stack: use STACK_INIT_OFFSET where possible

Make STACK_INIT_OFFSET also available for assembler code, and
use it everywhere instead of open-coding it at several places.

Reviewed-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
5 files changed