zynq: config: Enable CONFIG_SYS_NO_FLASH through defconfig

Enable config CONFIG_SYS_NO_FLASH through defconfig
for all zynq boards.

Signed-off-by: Siva Durga Prasad Paladugu <sivadur@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>