s390/kasan: avoid instrumentation of early C code

[ Upstream commit 0a9b40911baffac6fc9cc2d88e893585870a97f7 ]

Instrumented C code cannot run without the kasan shadow area. Exempt
source code files from kasan which are running before / used during
kasan initialization.

Reviewed-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>