ath79: add etactica-eg200 support

ath79: add etactica-eg200 support

Based on original ar71xx eg200 board files

Tested working:
* usb hub, storage and serial port
* ethernet
* wifi
* leds
* button

sysupgrade from self->self passes validity checks.
sysupgrade from old ar71xx->ath79 passes. (however this doesn't migrate
wireless driver configs)

Only unknown issue is the existance of a /sys/class/leds/ath9k-phy0,
which doesn't "exist"

Signed-off-by: Karl Palsson <karlp@etactica.com>