ramips: add support for Yuncore 1200F

ramips: add support for Yuncore 1200F

The Yuncore 1200F is an outdoor 802.11ac access point based on the
MediaTek MT7628AN SoC with an MT7663E PCIe 5 GHz radio. The device is
also sold under the KuWFi AP1200F name.

Hardware:
- SoC: MediaTek MT7628AN
- CPU: MIPS 24KEc
- RAM: 64 MiB
- Flash: 8 MiB SPI NOR
- Ethernet: 2x 10/100 Mbps
- WiFi 2.4 GHz: MT7628AN WMAC
- WiFi 5 GHz: MT7663E PCIe
- LEDs: status, LAN, WAN
- Button: reset
- Watchdog: GPIO watchdog

MAC addresses:
- Ethernet: factory 0x0004
- 2.4 GHz WiFi: factory 0x0028
- 5 GHz WiFi: factory 0x8004

Network:
- LAN: eth0.1, switch port 4
- WAN: eth0.2, switch port 3

Installation:
- Build the sysupgrade image:
  openwrt-ramips-mt76x8-yuncore_1200f-squashfs-sysupgrade.bin
- The stock firmware provides a U-Boot recovery web interface. It can be
  entered by holding the reset button while powering on the device. Connect to
  http://192.168.0.100/ and upload openwrt-sysupgrade.bin file.

Recovery:
- Reverting to stock firmware has not been tested.

The 5 GHz radio is detected as PCI ID 14c3:7663 and uses mt7615e
together with the MT7663 AP firmware. kmod-mt76x2 is explicitly
excluded because this board uses MT7663E, not MT76x2.

Tested:
- Build succeeds for ramips/mt76x8
- Sysupgrade image boots
- Ethernet LAN/WAN work
- 2.4 GHz AP starts on phy0
- 5 GHz AP starts on phy1
- Stable MAC addresses are assigned to Ethernet, phy0 and phy1

Signed-off-by: Gunther Stammwitz <gstammw@gmx.net>
Link: https://github.com/openwrt/openwrt/pull/23613
Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>