ASoC: SOF: imx: fix undefined reference issue

make.cross ARCH=mips allyesconfig fails with the following error:

sound/soc/sof/sof-of-dev.o:(.data.sof_of_imx8mp_desc+0x40): undefined
reference to `sof_imx8m_ops'

This seems to be a Makefile order issue, solve by using the same
structure as for Intel platforms.

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>

sound/soc/sof/imx/Kconfig

@@ -21,8 +21,7 @@ config SND_SOC_SOF_IMX8_SUPPORT
 	  If unsure select "N".
 
 config SND_SOC_SOF_IMX8
-	def_tristate SND_SOC_SOF_OF
-	depends on SND_SOC_SOF_IMX8_SUPPORT
+	tristate
 
 config SND_SOC_SOF_IMX8M_SUPPORT
 	bool "SOF support for i.MX8M"
@@ -33,6 +32,11 @@ config SND_SOC_SOF_IMX8M_SUPPORT
 	  If unsure select "N".
 
 config SND_SOC_SOF_IMX8M
+	tristate
+
+config SND_SOC_SOF_IMX
 	def_tristate SND_SOC_SOF_OF
-	depends on SND_SOC_SOF_IMX8M_SUPPORT
+	select SND_SOC_SOC_IMX8  if SND_SOC_SOF_IMX8_SUPPORT
+	select SND_SOC_SOC_IMX8M if SND_SOC_SOF_IMX8M_SUPPORT
+
 endif ## SND_SOC_SOF_IMX_IMX_TOPLEVEL