bcm53xx: add support for Phicomm K3

bcm53xx: add support for Phicomm K3

Hardware specifications:

- CPU: Broadcom BCM4709C0 @1.4GHz (Dual-Core ARM)
- RAM: 512 MB (DDR3)
- Flash: 128 MB (NAND)
- LAN ports: 3, LAN speed: 10/100/1000
- WAN ports: 1, WAN speed: 10/100/1000
- 2.4G: BCM4366 4x4 MIMO 1000Mbps -- Skyworks SE2623L 2.4GHz Power Amplifier (x4)
- 5G: BCM4366 4x4 MIMO 2167Mbps -- RFMD RFPA5542 5GHz Power Amplifier Module (x4)
- USB: 1x USB 3.0 port
- 1x LED, 1x reset button, 1x power switch
- 1x system status touch screen

Flash:

- Enter CFE
- Upload the trx file
- Reboot

Signed-off-by: Hao Dong <halbertdong@gmail.com>