Most architectures that support kprobes declare this function in their
own asm/kprobes.h header and provide an override, but some are missing
the prototype, which causes a warning for the __weak stub implementation:

kernel/kprobes.c:1865:12: error: no previous prototype for 'kprobe_exceptions_notify' [-Werror=missing-prototypes]
 1865 | int __weak kprobe_exceptions_notify(struct notifier_block *self,

Move the prototype into linux/kprobes.h so it is visible to all
the definitions.

Link: https://lore.kernel.org/all/20231108125843.3806765-4-arnd@kernel.org/Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>