ASoC: SOF: Introduce snd_sof_mailbox_read / snd_sof_mailbox_write callbacks

We need to introduce snd_sof_mailbox_{read/write} in order to provide
a generic way for mailbox access. These routines are optional, each
platform can implement their own specific routines.

So far, all platforms use mmapped I/O thus they can use custom made
routines sof_mailbox_read / sof_mailbox_write that use MMIO.

Signed-off-by: Daniel Baluta <daniel.baluta@nxp.com>
Signed-off-by: Bud Liviu-Alexandru <budliviu@gmail.com>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Reviewed-by: Péter Ujfalusi <peter.ujfalusi@linux.intel.com>
Link: https://lore.kernel.org/r/20211004152147.1268978-2-daniel.baluta@oss.nxp.com
Signed-off-by: Mark Brown <broonie@kernel.org>
diff --git a/sound/soc/sof/imx/imx8.c b/sound/soc/sof/imx/imx8.c
index 080dafb..195297b 100644
--- a/sound/soc/sof/imx/imx8.c
+++ b/sound/soc/sof/imx/imx8.c
@@ -421,6 +421,10 @@ struct snd_sof_dsp_ops sof_imx8_ops = {
 	.block_read	= sof_block_read,
 	.block_write	= sof_block_write,
 
+	/* Mailbox IO */
+	.mailbox_read	= sof_mailbox_read,
+	.mailbox_write	= sof_mailbox_write,
+
 	/* ipc */
 	.send_msg	= imx8_send_msg,
 	.fw_ready	= sof_fw_ready,
@@ -468,6 +472,10 @@ struct snd_sof_dsp_ops sof_imx8x_ops = {
 	.block_read	= sof_block_read,
 	.block_write	= sof_block_write,
 
+	/* Mailbox IO */
+	.mailbox_read	= sof_mailbox_read,
+	.mailbox_write	= sof_mailbox_write,
+
 	/* ipc */
 	.send_msg	= imx8_send_msg,
 	.fw_ready	= sof_fw_ready,