Convert CONFIG_CMD_THOR_DOWNLOAD to Kconfig

This converts the following to Kconfig:
   CONFIG_CMD_THOR_DOWNLOAD

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
diff --git a/configs/xilinx_zynqmp_zcu102_revA_defconfig b/configs/xilinx_zynqmp_zcu102_revA_defconfig
index c52b583..910cd1e 100644
--- a/configs/xilinx_zynqmp_zcu102_revA_defconfig
+++ b/configs/xilinx_zynqmp_zcu102_revA_defconfig
@@ -20,6 +20,7 @@
 CONFIG_SPL_OS_BOOT=y
 CONFIG_SYS_PROMPT="ZynqMP> "
 # CONFIG_CMD_IMLS is not set
+CONFIG_CMD_THOR_DOWNLOAD=y
 CONFIG_CMD_EEPROM=y
 CONFIG_CMD_MEMTEST=y
 CONFIG_CMD_UNZIP=y