u-boot: make the tools compile on OS X 10.9

Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>
u-boot GTA04: print device tree file name in early u-boot log

Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>
boot.scr: try flashing only if NAND read works (BB XM has variants with and w/o NAND)

Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>