ASoC: imx-card: support playback or capture only

Merge series from Shengjiu Wang <shengjiu.wang@nxp.com>:

Be similar to audio graph card, support playback or capture only for
imx-audio-card.

imx-card can't directly refer to audio-graph-port.yaml, because it is
not based on 'ports'. Add playback-only and capture-only property
directly