ASoC: imx: fix fiq dependencies

During randconfig builds, I occasionally run into an invalid configuration
of the freescale FIQ sound support:

WARNING: unmet direct dependencies detected for SND_SOC_IMX_PCM_FIQ
  Depends on [m]: SOUND [=y] && !UML && SND [=y] && SND_SOC [=y] && SND_IMX_SOC [=m]
  Selected by [y]:
  - SND_SOC_FSL_SPDIF [=y] && SOUND [=y] && !UML && SND [=y] && SND_SOC [=y] && SND_IMX_SOC [=m]!=n && (MXC_TZIC [=n] || MXC_AVIC [=y])

sound/soc/fsl/imx-ssi.o: In function `imx_ssi_remove':
imx-ssi.c:(.text+0x28): undefined reference to `imx_pcm_fiq_exit'
sound/soc/fsl/imx-ssi.o: In function `imx_ssi_probe':
imx-ssi.c:(.text+0xa64): undefined reference to `imx_pcm_fiq_init'

The Kconfig warning is a result of the symbol being defined inside of
the "if SND_IMX_SOC" block, and is otherwise harmless. The link error
is more tricky and happens with SND_SOC_IMX_SSI=y, which may or may not
imply FIQ support. However, if SND_SOC_FSL_SSI is set to =m at the same
time, that selects SND_SOC_IMX_PCM_FIQ as a loadable module dependency,
which then causes a link failure from imx-ssi.

The solution here is to make SND_SOC_IMX_PCM_FIQ built-in whenever
one of its potential users is built-in.

Fixes: ff40260f ("ASoC: fsl: refine DMA/FIQ dependencies")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Mark Brown <broonie@kernel.org>