[ARM] 5612/1: ep93xx: add platform LEDs

The EP93xx has two gpio pins specifically assigned to drive
external LEDs.  Add core support for these LEDs.

On the EDB93xx development boards, the rdled is connected to
an external reset circuit.  Turning this led on for an extended
amount of time will cause the circuit to issue a manual reset.

Refer to Cirrus App Note AN258 for more information.

	http://www.cirrus.com/en/pubs/appNote/AN258REV2.pdf

This led can be safely used as the system heartbeat with the
ledtrig-heartbeat driver.

	echo heartbeat > /sys/class/leds/platform:rdled/trigger

The grled can be used for any desired purpose.

Tested-by: Matthieu Crapet <mcrapet@gmail.com>
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>