ARM: OMAP: Add support for Amstrad Delta keypad

This adds support for the keypad on the top of the Amstrad Delta. It's
just a standard omap-keypad so all we need to do is add the keypad
layout and platform data to the board definition file.

Signed-off-by: Jonathan McDowell <noodles@earth.li>
Signed-off-by: Tony Lindgren <tony@atomide.com>