s390/cpum_sf: move functions from header file to source file

Some inline helper functions are defined in a header file but used
in only one source file. Move these functions to the source file.
No functional change.

Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>