zynq: Make CONFIG_OF_EMBED default case

Use embedded DTB to let users use u-boot instead of u-boot-dtb.bin.
And fix SPL to use this target.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/configs/zynq_zc770_xm010_defconfig b/configs/zynq_zc770_xm010_defconfig
index f1fc283..52511a7 100644
--- a/configs/zynq_zc770_xm010_defconfig
+++ b/configs/zynq_zc770_xm010_defconfig
@@ -11,4 +11,5 @@
 # CONFIG_CMD_IMLS is not set
 # CONFIG_CMD_FLASH is not set
 # CONFIG_CMD_SETEXPR is not set
+CONFIG_OF_EMBED=y
 CONFIG_SPI_FLASH=y