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/upgrade/platform.sh

@@ -144,6 +144,7 @@ platform_check_image() {
 	tew-714tru|\
 	timecloud|\
 	tiny-ac|\
+	u25awf-h1|\
 	ur-326n4g|\
 	ur-336un|\
 	v22rw-2x2|\