kconfig: zynq: Add ZYBO board

Add a defconfig and Kconfigury for the Digilent ZYBO board.

Signed-off-by: Peter Crosthwaite <crosthwaite.peter@gmail.com>
Acked-by: Jagannadha Sutradharudu Teki <jaganna@xilinx.com>
Reviewed-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/configs/zynq_zybo_defconfig b/configs/zynq_zybo_defconfig
new file mode 100644
index 0000000..a00f4fc
--- /dev/null
+++ b/configs/zynq_zybo_defconfig
@@ -0,0 +1,4 @@
+CONFIG_SPL=y
++S:CONFIG_ARM=y
++S:CONFIG_ZYNQ=y
++S:CONFIG_TARGET_ZYNQ_ZYBO=y