ASoC: zte: spdif and i2s drivers are not zx296702 specific

ZTE ZX SPDIF and I2S drivers can work on not only ZX296702 but also
other ZTE ZX family SoCs like ZX296718, which is an arm64 platform.
Let's make a few renaming and tweak the Kconfig a bit to get the drivers
available for other ZTE ZX platforms.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Reviewed-by: Jun Nie <jun.nie@linaro.org>
Signed-off-by: Mark Brown <broonie@kernel.org>