OMAP: Add gpio-leds support for Overo

This patch adds support for the standard LEDs on the Overo COM and expansion boards

Signed-off-by: Steve Sakoman <steve@sakoman.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>