ASoC: fsl_rpmsg: Add rpmsg audio support for i.MX8ULP

On i.MX8ULP the audio interface and codec are controlled
by Cortex-M domain, Cortex-M core provides audio service
over rpmsg.

The rpmsg audio function is almost same as i.MX7ULP
platform, so share same configuration.

Signed-off-by: Shengjiu Wang <shengjiu.wang@nxp.com>
Link: https://lore.kernel.org/r/1632972413-22130-1-git-send-email-shengjiu.wang@nxp.com


Signed-off-by: Mark Brown <broonie@kernel.org>