host-zynq-boot-bin: new package

The package provides a Python script that can create the file BOOT.BIN
to boot Xilinx Zynq based boards.

The script zynq-boot-bin.py is contained in the Xilinx repository of
U-Boot (it is not in upstream).

[Thomas:
 - remove appearance of the package in menuconfig, U-Boot will depend
   on it directly, so there's no need for it to appear in menuconfig
 - use $(INSTALL) instead of cp for the installation
 - remove @ before the extract and install commands.]

Signed-off-by: Jan Viktorin <viktorin@rehivetech.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>