ASoC: fix ES8328_I2C/SPI dependencies

The two front-ends to the codec can now be selected individually, but fail to
build when the bus support is missing:

sound/built-in.o: In function `es8328_spi_probe':
es8328-spi.c:(.text+0x125854): undefined reference to `__devm_regmap_init_spi'
sound/built-in.o: In function `es8328_spi_driver_init':
es8328-spi.c:(.init.text+0x3589): undefined reference to `__spi_register_driver'

Related to this, the added dependency on SND_SOC_ES8328 breaks:

warning: (SND_SOC_ALL_CODECS) selects SND_SOC_ES8328_I2C which has unmet direct dependencies (SOUND && !M68K && !UML && SND && SND_SOC && SND_SOC_ES8328 && I2C)

This adds the respective Kconfig dependencies and changes SND_SOC_ES8328 to a hidden
symbol that is selected implicitly by the two more specific options, as we do for
some other codecs. We have to remove the 'depends on' for SND_SOC_IMX_ES8328 in the
same step to avoid a recursive dependency.

Fixes: aa00f2c8 ("ASoC: Allow to select ES8328_I2C and ES8328_SPI directly")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Mark Brown <broonie@kernel.org>