ASoC: imx-hdmi-dma: Fix channel mapping ALSA <-> CEA

Map default ALSA channel allocation (see snd_pcm_std_chmaps[] in pcm_lib.c)
to HDMI/CEA-861D speaker locations. This patch only implements a single,
fixed mapping. In order to support all features, we need to add this:
https://www.kernel.org/doc/Documentation/sound/alsa/Channel-Mapping-API.txt

Signed-off-by: Rudi <r.ihle@s-t.de>