reset: sunxi: allow MFD subdevices probe

The current implementation uses sunxi_reset_init function for both early
init and platform device probe.

The sunxi_reset_init function uses DT to retrieve device resources, which
will be an issue if reset controllers are registered from an MFD device
that define resources from mfd_cell definition.

Moreover, we can make of devm functions when we're in the probe context.

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