ASoC: fsl: Fix module build

Building imx_v6_v7_defconfig with all audio drivers as modules results in
the folowing build error:

ERROR: "imx_pcm_fiq_init" [sound/soc/fsl/snd-soc-imx-ssi.ko] undefined!
ERROR: "imx_pcm_dma_init" [sound/soc/fsl/snd-soc-imx-ssi.ko] undefined!
ERROR: "imx_pcm_fiq_exit" [sound/soc/fsl/snd-soc-imx-ssi.ko] undefined!
ERROR: "imx_pcm_dma_exit" [sound/soc/fsl/snd-soc-imx-ssi.ko] undefined!
ERROR: "imx_pcm_dma_init" [sound/soc/fsl/snd-soc-fsl-ssi.ko] undefined!
ERROR: "imx_pcm_dma_exit" [sound/soc/fsl/snd-soc-fsl-ssi.ko] undefined!

Fix this by allowing SND_SOC_IMX_PCM_FIQ and SND_SOC_IMX_PCM_DMA to be also
built as modules and by using 'IS_ENABLED' to cover the module case.
Reported-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Mark Brown <broonie@linaro.org>

sound/soc/fsl/Kconfig

@@ -109,11 +109,11 @@ config SND_SOC_IMX_SSI
 	tristate
 
 config SND_SOC_IMX_PCM_FIQ
-	bool
+	tristate
 	select FIQ
 
 config SND_SOC_IMX_PCM_DMA
-	bool
+	tristate
 	select SND_SOC_GENERIC_DMAENGINE_PCM
 
 config SND_SOC_IMX_AUDMUX

sound/soc/fsl/imx-pcm.h

@@ -38,7 +38,7 @@ struct imx_pcm_fiq_params {
 	struct snd_dmaengine_dai_dma_data *dma_params_tx;
 };
 
-#ifdef CONFIG_SND_SOC_IMX_PCM_DMA
+#if IS_ENABLED(CONFIG_SND_SOC_IMX_PCM_DMA)
 int imx_pcm_dma_init(struct platform_device *pdev);
 void imx_pcm_dma_exit(struct platform_device *pdev);
 #else
@@ -52,7 +52,7 @@ static inline void imx_pcm_dma_exit(struct platform_device *pdev)
 }
 #endif
 
-#ifdef CONFIG_SND_SOC_IMX_PCM_FIQ
+#if IS_ENABLED(CONFIG_SND_SOC_IMX_PCM_FIQ)
 int imx_pcm_fiq_init(struct platform_device *pdev,
 		struct imx_pcm_fiq_params *params);
 void imx_pcm_fiq_exit(struct platform_device *pdev);