kprobes: introduce weak arch_check_ftrace_location() helper function

Introduce weak arch_check_ftrace_location() helper function which
architectures can override in order to implement handling of kprobes
on function tracer call sites on their own, without depending on
common code or implementing the KPROBES_ON_FTRACE feature.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>