ASoC: Constify static snd_pcm_hardware

Merge series from Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>:

Static 'struct snd_pcm_hardware' is not modified by few drivers and its
copy is passed to the core, so it can be made const for increased code
safety.

diff --cc sound/soc/fsl/imx-pcm-rpmsg.c
Simple merge

diff --cc sound/soc/meson/axg-fifo.c
Simple merge

diff --cc sound/soc/qcom/qdsp6/q6apm-dai.c
Simple merge