ftrace/samples: add s390 support for ftrace direct multi sample

Add s390 architecture support for the ftrace direct multi sample.
See commit 5fae941b ("ftrace/samples: Add multi direct interface
test module") for further details.

Link: https://lore.kernel.org/r/20211115195614.3173346-3-hca@linux.ibm.com


Signed-off-by: Heiko Carstens <hca@linux.ibm.com>