ASoC: Allow to select ES8328_I2C and ES8328_SPI directly

Currently, we have to select these symbols explictly via Kconfig, from
another entry. If we plan to use generic audio drivers like
simple-audio-card, the user need to be able to enable these symbols
directly via the menuconfig.

This commit also fixes unmet dependencies to SND_SOC_IMX_ES8328 caused
by these changes.

Signed-off-by: Romain Perier <romain.perier@collabora.com>
Signed-off-by: Mark Brown <broonie@kernel.org>