UPSTREAM: trace: Update documentation for mono, mono_raw and boot clock

UPSTREAM: trace: Update documentation for mono, mono_raw and boot clock

Documentation was missing for mono and mono_raw, add them and also for
the boot clock introduced in this series.

Bug: b/33184060

Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Prarit Bhargava <prarit@redhat.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Joel Fernandes <joelaf@google.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Acked-by: Steven Rostedt <rostedt@goodmis.org>