docs: ftrace: always use canonical ftrace path

The canonical location for the tracefs filesystem is at /sys/kernel/tracing.

But, from Documentation/trace/ftrace.rst:

  Before 4.1, all ftrace tracing control files were within the debugfs
  file system, which is typically located at /sys/kernel/debug/tracing.
  For backward compatibility, when mounting the debugfs file system,
  the tracefs file system will be automatically mounted at:

  /sys/kernel/debug/tracing

Many parts of Documentation still reference this older debugfs path, so
let's update them to avoid confusion.

Signed-off-by: Ross Zwisler <zwisler@google.com>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Link: https://lore.kernel.org/r/20230125213251.2013791-1-zwisler@google.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/admin-guide/pm/intel_pstate.rst

@@ -712,7 +712,7 @@ it works in the `active mode <Active Mode_>`_.
 The following sequence of shell commands can be used to enable them and see
 their output (if the kernel is generally configured to support event tracing)::
 
- # cd /sys/kernel/debug/tracing/
+ # cd /sys/kernel/tracing/
  # echo 1 > events/power/pstate_sample/enable
  # echo 1 > events/power/cpu_frequency/enable
  # cat trace
@@ -732,7 +732,7 @@ The ``ftrace`` interface can be used for low-level diagnostics of
 P-state is called, the ``ftrace`` filter can be set to
 :c:func:`intel_pstate_set_pstate`::
 
- # cd /sys/kernel/debug/tracing/
+ # cd /sys/kernel/tracing/
  # cat available_filter_functions | grep -i pstate
  intel_pstate_set_pstate
  intel_pstate_cpu_init