ipq806x: add support for Fortinet FAP-421E

ipq806x: add support for Fortinet FAP-421E

Hardware
--------

SoC:    Qualcomm IPQ8064
RAM:    235MB
Flash:  128MB NAND (Micron MT29F1G08ABBDAH4)
        32MB SPI-NOR (Spansion FL256SAIFRO)
WLAN2:  Qualcomm Atheros QCA9980
WLAN5:  Qualcomm Atheros QCA9980
ETH:    LAN1 - Atheros AR8035
        LAN2 - Atheros AR8033
USB:    USB-A, 2.0
LED:    Power (yellow/amber)
        LAN1 (yellow/amber)
        LAN2 (yellow/amber)
        WLAN2G (yellow)
        WLAN5G (yellow)
BTN:    Reset
Serial: RJ45 Port (9600 8n1) Cisco console cable, TTL voltage

MAC Address:    LAN1 (label) at APPSBL partition
                LAN2: label + 1
                WLAN2: label + 8
                WLAN5: label + 16

Installation
------------

Connect to the RJ45 console (TTL)
Connect LAN1 to host, set host ip as 192.168.1.10
Start a tftp server to serve the initramfs image
Open console connection (9600n8)
Connect power through the DC jack

`Hit any key to stop autoboot:  5`: press any key
`Enter G,Q,or H:`: press `K` to access the hidden option
`Enter password:`: `fap22b1!$` to access a limited u-boot console
`(FAP) #`: `tftpboot your_initramfs_image_name.itb`
`(FAP) #`: `bootm`

Once OpenWrt has booted, install the firmware through sysupgrade

Signed-off-by: JinGen Lim <openwrt@sn.sg>