ASoC: wm9712: Convert to regmap

Currently the wm9712 driver still uses custom snd_soc_codec_driver IO
callbacks. This has been deprecated for a while, so convert the wm9712
driver to use regmap for its IO.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Tested-by: Marek Vasut <marex@denx.de>
Acked-by: Marek Vasut <marex@denx.de>
Acked-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@kernel.org>