s390: use IS_ENABLED to check if a CONFIG is set to y or m

This is shorter and should be used instead of the longer form
which checks for both possible config options.

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

diff --cc arch/s390/kernel/entry64.S
Simple merge

diff --cc arch/s390/kernel/perf_event.c
Simple merge

diff --cc arch/s390/kernel/s390_ksyms.c
Simple merge