ath79: add support for Teltonika RUT300

ath79: add support for Teltonika RUT300

Add support for the Teltonika RUT300 rugged industrial Ethernet router

Hardware
--------
SoC:    Qualcomm Atheros QCA9531
RAM:    64M DDR2 (EtronTech EM68B16CWQK-25IH)
FLASH:  16M SPI-NOR (Winbond W25Q128)
ETH:    4x 100M LAN (QCA9533 internal AR8229 switch, eth0)
        1x 100M WAN (QCA9533 internal PHY, eth1)
UART:   115200 8n1, same debug port as other Teltonika devices
USB:    1 single USB 2.0 host port
BUTTON: Reset
LED:    1x green power LED (always on)
        5x yellow Ethernet port LED (controlled by Linux)
        WAN port LED is used as boot status and upgrade indicator as
        the power LED cannot be controlled in software.

Use the *-factory.bin file to intially flash the device using the
vendor firmware's Web-UI.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>