imx: Kconfig: enable IMX_BOOTAUX for i.MX8M

i.MX8M could use imx bootaux to boot m4/m7 core, so let's add it
to the dependency list.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
diff --git a/arch/arm/mach-imx/Kconfig b/arch/arm/mach-imx/Kconfig
index bed8cc7..6c3fedf 100644
--- a/arch/arm/mach-imx/Kconfig
+++ b/arch/arm/mach-imx/Kconfig
@@ -23,7 +23,7 @@
 
 config IMX_BOOTAUX
 	bool "Support boot auxiliary core"
-	depends on ARCH_MX7 || ARCH_MX6 || ARCH_VF610
+	depends on ARCH_MX7 || ARCH_MX6 || ARCH_VF610 || ARCH_IMX8M
 	help
 	  bootaux [addr] to boot auxiliary core.