two updates to the boot process

This patchset does two things

Firstly, it drops the compiled FDT file into /boot/kernel on the UFS file system, and configures u-boot to pass the name of the DTB file to ubldr.  This leverages some recent changes to ubldr and the fact that the Wandboard kernel no longer uses a statically linked FDT

Secondly, I was looking for a way to simplify the patch sets we apply to u-boot.  I've added a function to uboot.sh that uses the u-boot tool "mkimage" to pass boot instructions to u-boot.  This relieves us of the numerous patches that were applied to wandboard.h to configure the boot.  In the new system, boot instructions in /files/boot.txt are compiled using mkimage to boot.scr.  boot.scr is put on the FAT filesystem where u-boot finds it and executes the instructions.  My hope is that this method of configuring u-boot can be used for other boards, and that it will make it easier to configure u-boot and to update to new versions.