[BSP][qemu-vexpress-a9] add SOC chip type definition

bsp/qemu-vexpress-a9/Kconfig

@@ -17,4 +17,10 @@ config $PKGS_DIR
 
 source "$RTT_DIR/Kconfig"
 source "$PKGS_DIR/Kconfig"
+
+config SOC_VEXPRESS_A9
+    bool
+    select ARCH_ARM_CORTEX_A9
+    default y
+
 source "$BSP_DIR/drivers/Kconfig"