ath79: fix GL.iNet AR300M family GPIOs/LEDs

ath79: fix GL.iNet AR300M family GPIOs/LEDs

Change the "status" LED to proper GPIO 12 and "red" naming.

Remove GPIO 2 from definition as a USB LED.

GPIO 2 is used to control power to the USB socket, not an LED.
As such, PWM on the line or typical LED triggers are inappropriate.

Users who wish to control the USB power for custom applications
can manipulate the GPIO through code, or for example, export it
through /sys/class/gpio/export.

Runtime-tested:  GL.iNet AR300M-Lite

Signed-off-by: Jeff Kletsky <git-commits@allycomm.com>