imx8mm: Update CPU speed grading

According to iMX8MM datasheet (IMX8MMIEC_Rev_D and IMX8MMCEC_Rev_D),
the speed grading for imx8mm is 800Mhz, 1.2Ghz, 1.6Ghz and 1.8Ghz.
Update them to get_cpu_speed_grade_hz function.

Signed-off-by: Ye Li <ye.li@nxp.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Reviewed-by: Peng Fan <peng.fan@nxp.com>
diff --git a/arch/arm/mach-imx/cpu.c b/arch/arm/mach-imx/cpu.c
index bfa85c6..55e3539 100644
--- a/arch/arm/mach-imx/cpu.c
+++ b/arch/arm/mach-imx/cpu.c
@@ -332,11 +332,11 @@
 	case OCOTP_TESTER3_SPEED_GRADE0:
 		return 800000000;
 	case OCOTP_TESTER3_SPEED_GRADE1:
-		return is_mx7() ? 500000000 : 1000000000;
+		return (is_mx7() ? 500000000 : (is_imx8mq() ? 1000000000 : 1200000000));
 	case OCOTP_TESTER3_SPEED_GRADE2:
-		return is_mx7() ? 1000000000 : 1300000000;
+		return (is_mx7() ? 1000000000 : (is_imx8mq() ? 1300000000 : 1600000000));
 	case OCOTP_TESTER3_SPEED_GRADE3:
-		return is_mx7() ? 1200000000 : 1500000000;
+		return (is_mx7() ? 1200000000 : (is_imx8mq() ? 1500000000 : 1800000000));
 	}
 
 	return 0;