s390/tracing: Define ftrace_get_symaddr() for s390

Add ftrace_get_symaddr() for s390, which returns the symbol address
from ftrace's 'ip' parameter.

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Link: https://lore.kernel.org/r/173807818869.1854334.15474589105952793986.stgit@devnote2


Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>