ftrace: Add ftrace_add_rec_direct function

Factor out the code that adds (ip, addr) tuple to direct_functions
hash in new ftrace_add_rec_direct function. It will be used in
following patches.

Link: https://lkml.kernel.org/r/20211008091336.33616-6-jolsa@kernel.org



Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>