imx: add USB2_BOOT type

Add USB2_BOOT type for i.MX8ULP and i.MX9

Signed-off-by: Peng Fan <peng.fan@nxp.com>
diff --git a/arch/arm/include/asm/mach-imx/boot_mode.h b/arch/arm/include/asm/mach-imx/boot_mode.h
index 6dc5855..a568c44 100644
--- a/arch/arm/include/asm/mach-imx/boot_mode.h
+++ b/arch/arm/include/asm/mach-imx/boot_mode.h
@@ -29,6 +29,7 @@
 	QSPI_BOOT,
 	FLEXSPI_BOOT,
 	USB_BOOT,
+	USB2_BOOT,
 	UNKNOWN_BOOT,
 	BOOT_DEV_NUM = UNKNOWN_BOOT,
 };