add defconfig for qemu-arm vexpress

target/linux/Config.in.kernelcfg

@@ -54,6 +54,7 @@ config ADK_TARGET_LINUX_KERNEL_DEFCONFIG
 	default "loongson3_defconfig" if ADK_TARGET_SYSTEM_QEMU_LOONGARCH
 	default "defconfig" if ADK_TARGET_SYSTEM_ROCKPI4_PLUS
 	default "rockpi4_defconfig" if ADK_TARGET_SYSTEM_ROCKPI4_PLUS && ADK_TARGET_LINUX_KERNEL_VERSION_GIT
+	default "vexpress_defconfig" if ADK_TARGET_SYSTEM_QEMU_ARM_VEXPRESS_A9
 	default ""
 
 config ADK_TARGET_LINUX_KERNEL_CUSTOMCONFIG_PATH