xilinx: Add support for ENV_VARS_UBOOT_RUNTIME_CONFIG

Start to use ENV_VARS_UBOOT_RUNTIME_CONFIG to enable/disable updating
variables with run time information.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/board/xilinx/zynqmp/zynqmp.c b/board/xilinx/zynqmp/zynqmp.c
index 2a430a9..b4e7301 100644
--- a/board/xilinx/zynqmp/zynqmp.c
+++ b/board/xilinx/zynqmp/zynqmp.c
@@ -568,6 +568,9 @@
 		return 0;
 	}
 
+	if (!CONFIG_IS_ENABLED(ENV_VARS_UBOOT_RUNTIME_CONFIG))
+		return 0;
+
 	ret = set_fdtfile();
 	if (ret)
 		return ret;