ramips: add support for Kimax U25AWF-H1

Kimax U-25AWF-H1 is is a 2,5" HDD Enclosure with Wi-Fi/Eth conection
and battery, based on MediaTek MT7620A.

Patch rewritten from: https://forum.openwrt.org/viewtopic.php?pid=305643

Specification:

- MT7620A CPU
- 64 MB of RAM
- 16 MB of FLASH
- 802.11bgn WiFi
- 1x 10/100 Mbps Ethernet
- USB 2.0 Host
- UART for serial console

Flash instruction:
1. Download lede-ramips-mt7620-u25awf-h1-squashfs-sysupgrade.bin
2. Open webinterface a upgrade
3. After boot connect via ethernet to ip 192.168.1.1

Signed-off-by: Daniel Kucera <daniel.kucera@gmail.com>
[fix reset button gpio, don't add a lan/wan vlan config for single
port board, add -H1 suffix do make sure that this revision of the
board is supported/tested]
Signed-off-by: Mathias Kresin <dev@kresin.me>

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

@@ -505,6 +505,9 @@ ramips_board_detect() {
 	*"TL-WR841N v13")
 		name="tl-wr841n-v13"
 		;;
+	*"U25AWF-H1")
+		name="u25awf-h1"
+		;;
 	*"UBNT-ERX")
 		name="ubnt-erx"
 		;;