HID: add GPO (leds) support to PicoLCD device

Add leds support to PicoLCD device to drive the GPO pins.

GPO support depends on leds class and is only being
compiled if leds class has been selected.

Signed-off-by: Bruno Prémont <bonbons@linux-vserver.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>