OMAP3: BeagleBoard: add xM rev B to ID table

Patch was updated by Jason Kridner <jkridner@beagleboard.org>:
* Use tabs to match style of other board revisions
* Only include board revisions that exist
* Default to the same configuration as the latest revision, but
  without setting 'beaglerev'

Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>
Signed-off-by: Jason Kridner <jkridner@beagleboard.org>
Signed-off-by: Sandeep Paulraj <s-paulraj@ti.com>