lantiq: DGN3500: make switch LEDs blink on activity

Make switch port LEDs blink on activity as they do with stock firmware.

The u-boot loader sets suitable values in the LED control register that
unfortunately get blown away by the linux switch driver init.  Restore
that value by using driver 'initvals'.  0x0431 is the led control
register, the value 0x0960. Each nybble represents each LED's mode
(LED3,2,1,0) in this case OFF, 1000LINK+Activity, 100/10LINK+Activity,
OFF.  Only LED1&2 are physically present.

Enabling the blinkenlights exposed the fact that an RRCP packet was
being emitted by the switch on all ports every second.  Further initvals
copied from stock firmware's u-boot driver disabled this 'feature'.

Signed-off-by: Kevin Darbyshire-Bryant <kevin@darbyshire-bryant.me.uk>