dt-bindings:iio:adc:marvell,berlin2-adc yaml conversion

Part of a general move of IIO bindings over to yaml.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Cc: Antoine Tenart <antoine.tenart@free-electrons.com>
Link: https://lore.kernel.org/r/20200909175946.395313-6-jic23@kernel.org