arm: zynq: Enable bootz command for Xilinx platforms

bootz command is valid way how to boot Linux kernel. Enable it by
default.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/configs/zynq_zc706_defconfig b/configs/zynq_zc706_defconfig
index 8964f57..f14bed8 100644
--- a/configs/zynq_zc706_defconfig
+++ b/configs/zynq_zc706_defconfig
@@ -11,6 +11,7 @@
 CONFIG_SPL_OS_BOOT=y
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_PROMPT="Zynq> "
+CONFIG_CMD_BOOTZ=y
 CONFIG_CMD_THOR_DOWNLOAD=y
 CONFIG_CMD_EEPROM=y
 CONFIG_CMD_DFU=y