ASoC: fsl: select SND_SOC_IMX_PCM_DMA where needed

Since commit 204dec93 "ASoC: fsl: Allow to select individual common
options", it is possible to enable SND_SOC_FSL_SSI and SND_SOC_FSL_SPDIF
manually, either as loadable modules or built-in. This unfortunately
leads to a link error if one or both of them are built-in, while
the imx-pcm-dma framework is a loadable module:

sound/built-in.o: In function `fsl_ssi_probe':
:(.text+0x51fb8): undefined reference to `imx_pcm_dma_init'
sound/built-in.o: In function `fsl_spdif_probe':
:(.text+0x52e20): undefined reference to `imx_pcm_dma_init'

This changes Kconfig to prevent this case by using 'select' to turn
on the imx-pcm-dma code from both drivers. For consistency, we also
turn on the imx-pcm-fiq code, which is an alternative to the dma
implementation.

Note that imx-pcm-fiq is platform dependent, so we must not enable
that unless we are building a kernel for i.MX. Note also the
"if SND_IMX_SOC != n" syntax as opposed to the normal "if SND_IMX_SOC".
This is needed to avoid turning on the options as 'm' if 'SND_IMX_SOC'
is a module.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Mark Brown <broonie@linaro.org>