zynq_zc706: bump U-Boot to xilinx-v2016.2

zynq_zc706: bump U-Boot to xilinx-v2016.2

This is the latest release tag in the Xilinx repository, based on
U-Boot v2016.01 in the mainline.  It includes proper ps7_init_gpl.c/h
in it, so builds working SPL without any manual intervention.

BR2_TARGET_UBOOT_BOARD_NAME should be changed to zynq_zc706 since
U-Boot now has separate defconfig files for ZC702 and ZC706 boards.

BR2_TARGET_UBOOT_SPL_NAME should be changed to spl/boot.bin since
the Zynq image support for the mkimage tool was upstreamed and it
now generates boot.bin under spl/ directory.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Matt Weber <matthew.weber@rockwellcollins.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>