leds: add LED driver for EL15203000 board

This patch adds a LED class driver for the LEDs found on
the Crane Merchandising System EL15203000 LEDs board
(aka RED LEDs board).

Signed-off-by: Oleh Kravchenko <oleg@kaa.org.ua>
Reviewed-by: Dan Murphy <dmurphy@ti.com>
Signed-off-by: Pavel Machek <pavel@ucw.cz>