ASoC: Intel: sst: only use sst-firmware when DW DMAC is available

Currentlly, we use Synopsys DesignWare DMA Controller for
baytrail/haswell/broadwell ADSP firmware loading, but for
skylake, we don't use it, compiling sst-firmware.c may
introduce error when CONFIG_DW_DMAC_CORE is not enabled:

sound/built-in.o: In function `sst_dma_new':
(.text+0xd7b38): undefined reference to `dw_dma_probe'
sound/built-in.o: In function `sst_dma_free':
(.text+0xd7c0a): undefined reference to `dw_dma_remove'

Here we only compile sst-firmware when CONFIG_DW_DMAC_CORE
is selected, to fix the linking error issue.

Reported-by: Randy Dunlap <[e-mail]>
Signed-off-by: Jie Yang <[e-mail]>
Signed-off-by: Mark Brown <[e-mail]>

sound/soc/intel/common/Makefile

···
-snd-soc-sst-dsp-objs := sst-dsp.o sst-firmware.o
+snd-soc-sst-dsp-objs := sst-dsp.o
 snd-soc-sst-acpi-objs := sst-acpi.o
 snd-soc-sst-ipc-objs := sst-ipc.o
+
+ifneq ($(CONFIG_DW_DMAC_CORE),)
+snd-soc-sst-dsp-objs += sst-firmware.o
+endif
 
 obj-$(CONFIG_SND_SOC_INTEL_SST) += snd-soc-sst-dsp.o snd-soc-sst-ipc.o
 obj-$(CONFIG_SND_SOC_INTEL_SST_ACPI) += snd-soc-sst-acpi.o

sound/soc/intel/common/sst-dsp.c

···
 }
 EXPORT_SYMBOL_GPL(sst_dsp_inbox_read);
 
+#if IS_ENABLED(CONFIG_DW_DMAC_CORE)
 struct sst_dsp *sst_dsp_new(struct device *dev,
 	struct sst_dsp_device *sst_dev, struct sst_pdata *pdata)
 {
···
 	sst_dma_free(sst->dma);
 }
 EXPORT_SYMBOL_GPL(sst_dsp_free);
+#endif
 
 /* Module information */
 MODULE_AUTHOR("Liam Girdwood");

sound/soc/intel/common/sst-dsp.h

···
 	void *dsp;
 };
 
+#if IS_ENABLED(CONFIG_DW_DMAC_CORE)
 /* Initialization */
 struct sst_dsp *sst_dsp_new(struct device *dev,
 	struct sst_dsp_device *sst_dev, struct sst_pdata *pdata);
 void sst_dsp_free(struct sst_dsp *sst);
+#endif
 
 /* SHIM Read / Write */
 void sst_dsp_shim_write(struct sst_dsp *sst, u32 offset, u32 value);