ARM OMAP3: Initial support for Nokia RX-51, v3

Adds board files and related headers for Nokia RX-51
Internet Tablet.

This patch has been updated with some clean-up patches
posted earlier to linux-omap list.

Signed-off-by: Lauri Leukkunen <lauri.leukkunen@nokia.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>