ramips: add support for Planex VR500.

SOC:	MT7621A
RAM:	256MiB
NOR:	MX25L51245G

Non Wireless Router.

Issue: soft reboot problem. SPI Flash do not exit 4byte address mode.

Signed-off-by: Yuhei Okawa <tochiro.srchack@gmail.com>

target/linux/ramips/base-files/lib/ramips.sh

@@ -442,6 +442,9 @@ ramips_board_detect() {
 	*"VoCore")
 		name="vocore"
 		;;
+	*"VR500")
+		name="vr500"
+		;;
 	*"W150M")
 		name="w150m"
 		;;