ramips: add support for Mofi 5500

ramips: add support for Mofi 5500

Specifications:

SoC: Mediatek MT7621AT (880 MHz MIPS dual-core, quad-thread, CPU)
512 Megabyte DDR3 SDRAM
32 Megabyte NOR Flash
4 Gigabit RJ45 PoE ports
2 MT7615N wifi chips (2.4GHz and 5GHz)
2 USB ports (1xUSB2 and 1xUSB3 - GL3510 chip)
RJ45 RS232 port on front panel (Max3232 chip)
2x mPCIe 2.0 slots for 4G/5G cards
2x SIM slot
1x SDCard Slot
Power via DC12V
4x Cell Antennae
4x Wifi Antennae

MAC Address Locations:
Purpose	Ex.		Partition	Offset
2.4 Ghz	*:01	factory		0x4
5 GHz	*:02	factory		0x8004
LAN		*:03	factory		0xe000
WAN		*:04	factory		0xe006

MAC address prefix E4:3A:65 is registered to MofiNetwork Inc
and used as the prefix for all MAC addresses.

Manual: https://mofinetwork.com/files/MoFi_Network_MOFI5500_5GXeLTE_EM7690_SPECS.pdf
WiFi chip specs: https://www.mediatek.com/products/broadband-wifi/mt7615
CPU chip specs: https://www.mediatek.com/products/home-networking/mt7621
Teardown Pictures: https://fccid.io/2AE6X-MOFI5500/Internal-Photos/Internal-Photos-5591739

Installation:

Update Mofi 5500 to at least stock firmware version 4.8.6. (Available on the Mofi website.)
Previous versions are untested in the upgrade process. Log into the LuCI web interface,
usually at 192.168.10.1 and visit the 'System->Backup/Flash Firmware' page.
Upload and flash the firmware as usual.

Note to Maintainers: Do not remove SUPPORTED_DEVICES from the Makefile!
The customized Mofi version of OpenWRT (stock firmware) expects to see mofi5500 as the device
name. The stock firmware does not allow for forcing an installation.
Without this line, users cannot upload the new firmware through the stock Mofi firmware.

This device uses cell modems that could use QMI or MBIM.
Add LuCI Modem Manager to allow people to use these. Also, if they have
two cell network cards, ethernet, USB, or other kinds of networks, they may wish
to use MWAN3 to allow failover amongst their networks.

Please compile it with mwan3 for multiple WAN connections.

Co-authored-by: Mieczyslaw Nalewaj <namiltd@yahoo.com>
Signed-off-by: Rick Mac Gillis <noreply@rickmacgillis.com>