ASoC: SOF: add a field to store the current D0 substate of DSP

Add field d0_substate to struct snd_sof_dev to store the current DSP
D0 sub-state(only meaningful when DSP in D0), which could be D0I0 or
D0I3.
Signed-off-by: Keyon Jie <yang.jie@linux.intel.com>
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20191025224122.7718-2-pierre-louis.bossart@linux.intel.comSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/sof/sof-priv.h

@@ -68,6 +68,12 @@ extern int sof_core_debug;
 
 #define DMA_CHAN_INVALID	0xFFFFFFFF
 
+/* DSP D0ix sub-state */
+enum sof_d0_substate {
+	SOF_DSP_D0I0 = 0,	/* DSP default D0 substate */
+	SOF_DSP_D0I3,		/* DSP D0i3(low power) substate*/
+};
+
 struct snd_sof_dev;
 struct snd_sof_ipc_msg;
 struct snd_sof_ipc;
@@ -387,6 +393,9 @@ struct snd_sof_dev {
 	 */
 	struct snd_soc_component_driver plat_drv;
 
+	/* power states related */
+	enum sof_d0_substate d0_substate;
+
 	/* DSP firmware boot */
 	wait_queue_head_t boot_wait;
 	u32 boot_complete;