reset: Move DT cell size check to the core

The core currently doesn't check that the DT cell size matches what the
driver declares, which means that every xlate function needs to duplicate
that check.

Make sure that of_reset_control_get checks for this to avoid duplication
and errors.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>