MLK-15043-1: ASoC: soc-pcm: add dpcm_merged_chan in snd_soc_dai_link

MLK-15043-1: ASoC: soc-pcm: add dpcm_merged_chan in snd_soc_dai_link

According to commit b073ed4e2126 ("ASoC: soc-pcm: DPCM cares BE format"),
Current DPCM only care FE channel, but it will set unsupported channel to
drivers.
So add dpcm_merged_chan, which is used to merge the BE's codec
channels configuration to FE if it exist in snd_soc_dai_link. And
dpcm_runtime_base_chan function is to get the channel configuration of BE,
which likes the dpcm_runtime_base_format function.

Signed-off-by: Shengjiu Wang <shengjiu.wang@freescale.com>
(cherry picked from commit 19ff1095d4b68d17a5f68a2de5654be72b606809)