mfd: lochnagar: Add support for the Cirrus Logic Lochnagar

Lochnagar is an evaluation and development board for Cirrus
Logic Smart CODEC and Amp devices. It allows the connection of
most Cirrus Logic devices on mini-cards, as well as allowing
connection of various application processor systems to provide a
full evaluation platform. This driver supports the board
controller chip on the Lochnagar board. Audio system topology,
clocking and power can all be controlled through the Lochnagar
controller chip, allowing the device under test to be used in
a variety of possible use cases.

As the Lochnagar is a fairly complex device this MFD driver
allows the drivers for the various features to be bound
in. Initially clocking, regulator and pinctrl will be added as
these are necessary to configure the system. But in time at least
audio and voltage/current monitoring will also be added.

Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>