ARM: OMAP1: ams-delta: supersede custom led device by leds-gpio

Now that the Amstrad Delta on-board latches have been converted to GPIO
devices, use the generic driver to control on-board LEDs which hang off
those latches.

Signed-off-by: Janusz Krzysztofik <jkrzyszt@tis.icnet.pl>
Signed-off-by: Tony Lindgren <tony@atomide.com>