rtla/osnoise: Add an option to set the threshold

rtla/osnoise: Add an option to set the threshold

Add the -T/--threshold option to set the minimum threshold to be
considered a noise to osnoise top and hist commands. Also update
the man pages.

Link: https://lkml.kernel.org/r/031861200ffdb24a1df4aa72c458706889a20d5d.1646247211.git.bristot@kernel.org
Cc: Daniel Bristot de Oliveira <bristot@kernel.org>
Cc: Clark Williams <williams@redhat.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>