reset: mpfs: use the auxiliary device creation

The auxiliary device creation of this driver is simple enough to
use the available auxiliary device creation helper.

Use it and remove some boilerplate code.

Acked-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Link: https://lore.kernel.org/r/20250611-rst-mpfs-aux-v1-1-c86534b473c3@baylibre.com


Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>