Documentation: bindings: move the Berlin reset documentation

The Berlin reset documentation was part of the Marvell Berlin SoC
documentation because the Berlin reset configuration was inside the chip
controller. With the recent rework of the chip and system controller
handling (now an MFD driver registers all sub-devices of the two soc and
system controller nodes and each device has its own sub-node), the
documentation of the Berlin reset driver can be moved to the generic
reset documentation directory.

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>