imx: define ARCH_MXC for i.MX8/8M/7ULP

Without this definition, fsl_esdhc will access reserved registers
on i.MX chips, so define ARCH_MXC to fix it.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
diff --git a/arch/arm/include/asm/arch-imx8/imx-regs.h b/arch/arm/include/asm/arch-imx8/imx-regs.h
index af0fb51..6333ff4 100644
--- a/arch/arm/include/asm/arch-imx8/imx-regs.h
+++ b/arch/arm/include/asm/arch-imx8/imx-regs.h
@@ -6,6 +6,8 @@
 #ifndef __ASM_ARCH_IMX8_REGS_H__
 #define __ASM_ARCH_IMX8_REGS_H__
 
+#define ARCH_MXC
+
 #define LPUART_BASE		0x5A060000
 
 #define GPT1_BASE_ADDR		0x5D140000