s390/syscalls: add Makefile to generate system call header files

Generate the system call specific files from the archheaders
and archprepare make targets.

Signed-off-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Acked-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>