ASoC: imx-card: Add playback_only or capture_only support

ASoC: imx-card: Add playback_only or capture_only support

With the DPCM case, the backend only support capture or playback, then
the linked frontend can only support capture or playback, but frontend
can't automatically enable only capture or playback, it needs the input
from dt-binding.

Signed-off-by: Shengjiu Wang <shengjiu.wang@nxp.com>
Reviewed-by: Daniel Baluta <daniel.baluta@nxp.com>
Reviewed-by: Iuliana Prodan <iuliana.prodan@nxp.com>
Link: https://patch.msgid.link/20250217021715.284951-3-shengjiu.wang@nxp.com
Signed-off-by: Mark Brown <broonie@kernel.org>