kprobes: Fix to init kprobes in subsys_initcall

kprobes: Fix to init kprobes in subsys_initcall

Since arm64 kernel initializes breakpoint trap vector in arch_initcall(),
initializing kprobe (and run smoke test) in postcore_initcall() causes
a kernel panic.

To fix this issue, move the kprobe initialization in subsys_initcall()
(which is called right afer the arch_initcall).

In-kernel kprobe users (ftrace and bpf) are using fs_initcall() which is
called after subsys_initcall(), so this shouldn't cause more problem.

Link: http://lkml.kernel.org/r/155956708268.12228.10363800793132214198.stgit@devnote2
Link: http://lkml.kernel.org/r/20190709153755.GB10123@lakrids.cambridge.arm.com
Reported-by: Anders Roxell <anders.roxell@linaro.org>
Fixes: b5f8b32c93b2 ("kprobes: Initialize kprobes at postcore_initcall")
Tested-by: Anders Roxell <anders.roxell@linaro.org>
Tested-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>