reset: berlin: convert to a platform driver

The Berlin reset controller was introduced without being a platform
driver because of a needed DT rework: the node describing the reset
controller also describes the pinctrl and clk controllers...

Prepare conversion by adding a platform driver probe to a new
compatible "marvell,berlin2-reset" with syscon regmap.

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