buildroot

zynq_zc706: bump to U-Boot xilinx-v2017.1 (fix build)

The Zynq ZC706 defconfig does not build anymore since commit
6cda724efb20682bb98e6d738e5f7c909415ae07 ("package/gcc: switch to gcc
6.x as the default"). Fix by upgrading to the latest U-Boot version,
xilinx-v2017.1, based on mainline v2017.01.

Fixes:
  In file included from include/linux/compiler.h:54:0,
                   from include/linux/bitops.h:5,
                   from ./include/common.h:20:
  include/linux/compiler-gcc.h:114:30: fatal error: linux/compiler-gcc6.h: No such file or directory
   #include gcc_header(__GNUC__)
                                ^
  compilation terminated.

[Build-tested only]
Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Alistair Francis <alistair.francis@xilinx.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>