gpio: madera: Support Cirrus Logic Madera class codecs

This adds support for the GPIOs on Cirrus Logic Madera class codecs.
Any pins not used for special functions (see the pinctrl driver) can be
used as general single-bit input or output lines. The number of available
GPIOs varies between codecs.

Note that this is part of a composite MFD for these codecs and can only
be used with the corresponding MFD and other child drivers on those
silicon. The GPIO block on these codecs does not exist indepedently of
the rest of the MFD.

Signed-off-by: Nariman Poushin <nariman@opensource.cirrus.com>
Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>