ASoC: SOF: i.MX: simplify Kconfig

Follow the Intel example and simplify the Kconfig
a) start from the end-product for 'select' chains
b) use 'depends on' to filter out configurations.
c) use snd-sof-of as a common module without any 'select'

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Reviewed-by: Daniel Baluta <daniel.baluta@nxp.com>
Signed-off-by: Daniel Baluta <daniel.baluta@nxp.com>
Link: https://lore.kernel.org/r/20211116124131.46414-1-daniel.baluta@oss.nxp.com
Signed-off-by: Mark Brown <broonie@kernel.org>