tools/bootconfig: Use per-group/all enable option in ftrace2bconf script

Use per-group/all enable option instead of ftrace.events option.
This will make the bootconfig file more readable.

Link: https://lkml.kernel.org/r/162856129436.203126.12462564671412940618.stgit@devnote2

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