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_zc770_xm012_defconfig b/configs/zynq_zc770_xm012_defconfig
index 71b379a..c62bdb1 100644
--- a/configs/zynq_zc770_xm012_defconfig
+++ b/configs/zynq_zc770_xm012_defconfig
@@ -12,6 +12,7 @@
 CONFIG_SPL_OS_BOOT=y
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_PROMPT="Zynq> "
+CONFIG_CMD_BOOTZ=y
 CONFIG_CMD_IMLS=y
 CONFIG_CMD_FPGA_LOADBP=y
 CONFIG_CMD_FPGA_LOADFS=y