arm: imx: add i.MX8ULP cpu type and helper

Add i.MX8ULP cpu type and helpers.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
diff --git a/arch/arm/include/asm/arch-imx/cpu.h b/arch/arm/include/asm/arch-imx/cpu.h
index 267a094..fe96378 100644
--- a/arch/arm/include/asm/arch-imx/cpu.h
+++ b/arch/arm/include/asm/arch-imx/cpu.h
@@ -50,8 +50,12 @@
 #define MXC_CPU_IMX8QXP_A0	0x90 /* dummy ID */
 #define MXC_CPU_IMX8QM		0x91 /* dummy ID */
 #define MXC_CPU_IMX8QXP		0x92 /* dummy ID */
+
+#define MXC_CPU_IMX8ULP		0xA1 /* dummy ID */
+
 #define MXC_CPU_IMXRT1020	0xB4 /* dummy ID */
 #define MXC_CPU_IMXRT1050	0xB6 /* dummy ID */
+
 #define MXC_CPU_MX7ULP		0xE1 /* Temporally hard code */
 #define MXC_CPU_VF610		0xF6 /* dummy ID */