doc-dyndbg: edit dynamic-debug-howto for brevity, audience

Rework/modernize docs:

 - use /proc/dynamic_debug/control in examples
   its *always* there (when dyndbg is config'd), even when <debugfs> is not.
   drop <debugfs> talk, its a distraction here.

 - alias ddcmd='echo $* > /proc/dynamic_debug/control
   focus on args: declutter, hide boilerplate, make pwd independent.

 - swap sections: Viewing before Controlling. control file as Catalog.

 - focus on use by a system administrator
   add an alias to make examples more readable
   drop grep-101 lessons, admins know this.

 - use init/main.c as 1st example, thread it thru doc where useful.
   everybodys kernel boots, runs these.

 - add *prdbg* api section
   to the bottom of the file, its for developers more than admins.
   move list of api functions there.

 - simplify - drop extra words, phrases, sentences.

 - add "decorator" flags line to unify "prefix", trim fmlt descriptions

CC: linux-doc@vger.kernel.org
Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
Link: https://lore.kernel.org/r/20220904214134.408619-20-jim.cromie@gmail.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>