imx: cpu: enlarge bit mask to 0x1FF for cpu type

i.MX8MP use 0x182 as dummy id, 0xFF is not able the get the highest
bit, so enlarge bit mask to 0x1FF to make it could detect
cpu type correctly

Signed-off-by: Peng Fan <peng.fan@nxp.com>
diff --git a/arch/arm/mach-imx/cpu.c b/arch/arm/mach-imx/cpu.c
index 303f5bb..bfa85c6 100644
--- a/arch/arm/mach-imx/cpu.c
+++ b/arch/arm/mach-imx/cpu.c
@@ -159,7 +159,7 @@
 	int cpu_tmp, minc, maxc, ret;
 
 	printf("CPU:   Freescale i.MX%s rev%d.%d",
-	       get_imx_type((cpurev & 0xFF000) >> 12),
+	       get_imx_type((cpurev & 0x1FF000) >> 12),
 	       (cpurev & 0x000F0) >> 4,
 	       (cpurev & 0x0000F) >> 0);
 	max_freq = get_cpu_speed_grade_hz();
@@ -171,7 +171,7 @@
 	}
 #else
 	printf("CPU:   Freescale i.MX%s rev%d.%d at %d MHz\n",
-		get_imx_type((cpurev & 0xFF000) >> 12),
+		get_imx_type((cpurev & 0x1FF000) >> 12),
 		(cpurev & 0x000F0) >> 4,
 		(cpurev & 0x0000F) >> 0,
 		mxc_get_clock(MXC_ARM_CLK) / 1000000);