bootconfig: Show the number of nodes on boot message

Show the number of bootconfig nodes on boot message.

Link: http://lkml.kernel.org/r/158091062297.27924.9051634676068550285.stgit@devnote2



Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>