ASoC: fsl: SND_SOC_FSL_AUD2HTX should depend on ARCH_MXC

The Freescale/NXP AUDIO TO HDMI TX module is only present on NXP i.MX 8
Series SoCs.  Hence add a dependency on ARCH_MXC, to prevent asking the
user about this driver when configuring a kernel without i.MX 8 platform
support.

Fixes: 8a24c834c0 ("ASoC: fsl_aud2htx: Add aud2htx module driver")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20201110145120.3280658-1-geert+renesas@glider.be
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/fsl/Kconfig

@@ -107,6 +107,7 @@ config SND_SOC_FSL_XCVR
 
 config SND_SOC_FSL_AUD2HTX
 	tristate "AUDIO TO HDMI TX module support"
+	depends on CONFIG_ARCH_MXC || COMPILE_TEST
 	help
 	  Say Y if you want to add AUDIO TO HDMI TX support for NXP.