The i.MX8MP AudioMix reset controller is only present on Freescale i.MX8
SoCs.  Hence add a dependency on ARCH_MXC, to prevent asking the user
about this driver when configuring a kernel without i.MX SoC support.

Fixes: fe125601 ("reset: imx8mp-audiomix: Add AudioMix Block Control reset driver")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
Link: https://lore.kernel.org/r/6d8116a56186fbf468229e823c7c8dfcd9488959.1719316665.git.geert+renesas@glider.beSigned-off-by: Philipp Zabel <p.zabel@pengutronix.de>