tracing: add options directory and core option files

This patch creates an options directory in the debugfs, that contains
the available tracing options. These files contain 1 or 0, where 1
is the option is enabled and 0 it is disabled.

Simply echoing in 1 will enable the option and 0 will disable it.
This patch only contains the core options, not the tracer options.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>