mfd: madera: Add Madera core support for CS47L15

This patch adds all the core support and defines for the Cirrus
Logic CS47L15 smart audio CODEC.

Registers or fields are named MADERA_* if it is part of the
common hardware platform and does not conflict with any other
Madera codecs. It is named CS47L15_* if it is unique to CS47L15
and conflicts with definitions on other codecs.

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