Documentation/auxiliary_bus: Clarify auxiliary_device creation

Documentation/auxiliary_bus: Clarify auxiliary_device creation

The documentation for creating an auxiliary device is a 3 step not a 2
step process.  Specifically the requirements of setting the name, id,
dev.release, and dev.parent fields was not clear as a precursor to the '2
step' process documented.

Clarify by declaring this a 3 step process starting with setting the
fields of struct auxiliary_device correctly.

Also add some sample code and tie the change into the rest of the
documentation.

Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Link: https://lore.kernel.org/r/20211202044305.4006853-2-ira.weiny@intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>