[beagleboard] [RFC] BeagleBoard: U-boot: Added LED driver and ramdisk

Added LED driver using status_led. USR0 is set to monitor the boot
status. USR1 is set to be the GREEN LED.

To simplify booting into various boot configurations, there is now a
test for an existing ramdisk.gz image if loading the boot script fails.
Adding additional boot arguments can also be done using optargs.

Signed-off-by: Jason Kridner <jkridner@beagleboard.org>