reset: add the Berlin reset controller driver

Add a reset controller for Marvell Berlin SoCs which is used by the
USB PHYs drivers (for now).

Signed-off-by: Antoine Ténart <antoine.tenart@free-electrons.com>
Acked-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>