[S390] Move private simple udelay function to arch/s390/lib/delay.c.

Move cio's private simple udelay function to lib/delay.c and turn it
into something much more readable. So we have all implementations
at one place.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>