ramips: add support for TP-Link Archer C2

Specification:

- System-On-Chip: MT7620A
- CPU/Speed: 580 MHz
- Flash-Chip: Winbond 25Q64BVSIG
- Flash size: 8192 KiB
- RAM: 64 MiB
- Wireless No1: SoC-integrated: MT7620A 2.4GHz 802.11bgn
- Wireless No2: On-board chip: MT7610EN 5GHz 802.11ac
- Switch: RTL8367RB Gigabit Switch
- USB: Yes 1 x 2.0

Preparing a TFTP recovery image for initial flashing:

Currently the only method to install openwrt for the first time is via
TFTP download in u-boot. After first install you can use regular updates.
WARNING: This method also overwrites the bootloader partition!

Create a TFTP recovery image:

1) Download a stock TP-Link Firmware file here:
     https://www.tp-link.com/en/download/Archer-C2_V1.html#Firmware
2) Extract u-boot from the binary file:
     #> dd if=c2v1_stock_firmware.bin of=c2v1_uboot.bin bs=1 skip=512 count=131072
3) Now merge the sysupgrade image and the u-boot into one binary:
     #> cat c2v1_uboot.bin openwrt-squashfs-sysupgrade.bin > ArcherC2V1_tp_recovery.bin

The resulting image can be flashed via TFTP recovery mode.

Flash instructions:

1) To flash the recovery image, start a TFTP server from IP address
   192.168.0.66 and serve the recovery image named
   ArcherC2V1_tp_recovery.bin.
2) Connect your device to the LAN port, then press the WPS/Reset button
   and power it up. Keep pressing the WPS/Reset button for 10 seconds.
   It will try to download the recovery image and flash it.

It can take up to 20-25 minutes to finish. When it reaches 100%, the
router will reboot itself.

Signed-off-by: Serge Vasilugin <vasilugin@yandex.ru>
Signed-off-by: Franz Flasch <franz.flasch@gmx.at>

target/linux/ramips/base-files/etc/board.d/01_leds

@@ -398,6 +398,12 @@ tl-wr841n-v13)
 	ucidef_set_led_switch "lan4" "lan4" "$boardname:green:lan4" "switch0" "0x10"
 	ucidef_set_led_switch "wan" "wan" "$boardname:green:wan" "switch0" "0x01"
 	;;
+tplink,c2-v1)
+	ucidef_set_led_switch "lan" "lan" "$boardname:green:lan" "switch1" "0x1e"
+	ucidef_set_led_switch "wan" "wan" "$boardname:green:wan" "switch1" "0x01"
+	set_usb_led "$boardname:green:usb" "2-1"
+	set_wifi_led "$boardname:green:wlan"
+	;;
 tplink,c20-v1)
 	ucidef_set_led_switch "lan" "lan" "$boardname:blue:lan" "switch0" "0x1e"
 	ucidef_set_led_switch "wan" "wan" "$boardname:blue:wan" "switch0" "0x01"

target/linux/ramips/base-files/etc/board.d/02_network

@@ -335,6 +335,10 @@ ramips_setup_interfaces()
 		ucidef_add_switch "switch0" \
 			"1:lan" "2:lan" "3:lan" "4:lan" "5:wan" "0@eth0"
 		;;
+	tplink,c2-v1)
+		ucidef_add_switch "switch1" \
+			"1:lan" "2:lan" "3:lan" "4:lan" "0:wan" "6@eth0"
+		;;
 	tplink,tl-wr902ac-v3)
 		ucidef_add_switch "switch0" \
 			"4:lan" "6@eth0"

target/linux/ramips/base-files/etc/diag.sh

@@ -79,6 +79,7 @@ get_status_led() {
 	awapn2403|\
 	dir-645|\
 	sk-wb8|\
+	tplink,c2-v1|\
 	wrh-300cr)
 		status_led="$boardname:green:wps"
 		;;

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

@@ -253,6 +253,7 @@ platform_check_image() {
 	c20i|\
 	c50|\
 	mr200|\
+	tplink,c2-v1|\
 	tplink,c20-v1|\
 	tplink,c20-v4|\
 	tplink,c50-v3|\