U-Boot loader for BeagleBone and BeagleBone Black.

This version is patched so that:
 * ELF and API features are enabled
 * U-Boot binary is called BB-UBOOT.IMG
 * It loads env from BB-UENV.TXT (an empty file suffices)
 * It loads BBONE.DTB if running on an older (white) BeagleBone,
   or BBONEBLK.DTB if running on a BeagleBone Black
 * By default, it loads ELF ubldr from file BBUBLDR to address 0x88000000

Note: prefixing the boot files with 'BB' allows building
images with boot bits for more than one board.

For information about running FreeBSD on BeagleBone or BeagleBone Black, see
 https://wiki.freebsd.org/FreeBSD/arm/BeagleBone

For general information about U-Boot, see
WWW: http://www.denx.de/wiki/U-Boot