ramips: WAN LED for D-Link DIR-300-B1

Add led devices for D-Link DIR-300-B1 WAN LED.

Note that the GPIO state is also ANDed with the esw switch port 4
LED state, which is why I've set the amber LED to default-on.

Closes: https://dev.openwrt.org/ticket/11326



Signed-off-by: Tobias Diedrich <ranma+openwrt@tdiedrich.de>

[ juhosg:
- fix comment style in mach-dir-300-revb.c,
- remove the PPP specific LED setup, not everyone uses a PPP connection
  on the WAN interface]

SVN-Revision: 31989