ASoC: wm8985: add support for WM8758

The WM8758 chip is almost identical to WM8985 with the difference that it
doesn't feature the AUX input. This patch adds the WM8758 support into the
WM8985 driver.

The chip selection is done by the I2C name. The SPI probe supports only
the WM8985.

Signed-off-by: Petr Kulhavy <petr@barix.com>
Reviewed-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@kernel.org>