imx8mn: support get_cpu_rev

Add a dummy cpu type and support get_cpu_rev for i.MX8MN

Signed-off-by: Peng Fan <peng.fan@nxp.com>
diff --git a/arch/arm/mach-imx/imx8m/soc.c b/arch/arm/mach-imx/imx8m/soc.c
index a924af4..82fa7ae 100644
--- a/arch/arm/mach-imx/imx8m/soc.c
+++ b/arch/arm/mach-imx/imx8m/soc.c
@@ -197,7 +197,9 @@
 	reg &= 0xff;
 
 	/* i.MX8MM */
-	if (major_low == 0x41) {
+	if (major_low == 0x42) {
+		return (MXC_CPU_IMX8MN << 12) | reg;
+	} else if (major_low == 0x41) {
 		type = get_cpu_variant_type(MXC_CPU_IMX8MM);
 	} else {
 		if (reg == CHIP_REV_1_0) {