regulator: wm8994: Pass descriptor instead of GPIO number

Instead of passing a global GPIO number for the enable GPIO, pass
a descriptor looked up from the device tree node or the board file
decriptor table for the regulator.

There is a single board file passing the GPIOs for LDO1 and LDO2
through platform data, so augment this to pass descriptors
associated with the i2c device as well.

The special GPIO enable DT property for the enable GPIO is
nonstandard but this was accomodated in
commit 6a537d48


"gpio: of: Support regulator nonstandard GPIO properties".

Cc: patches@opensource.cirrus.com
Acked-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Acked-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Mark Brown <broonie@kernel.org>