siox: Provide a devm variant of siox_master_alloc()

This allows to simplify siox master drivers in the next step.

Acked-by: Thorsten Scherer <t.scherer@eckelmann.de>
Link: https://lore.kernel.org/r/ad141dd22c7d95ad0bd347f257ce586e1afb22a4.1708328466.git.u.kleine-koenig@pengutronix.de


Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>