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/trats2_defconfig b/configs/trats2_defconfig
index 16ac27f..f91ec1d 100644
--- a/configs/trats2_defconfig
+++ b/configs/trats2_defconfig
@@ -13,6 +13,7 @@
 CONFIG_CMD_BOOTZ=y
 # CONFIG_CMD_IMLS is not set
 # CONFIG_CMD_XIMG is not set
+CONFIG_CMD_THOR_DOWNLOAD=y
 CONFIG_CMD_GPT=y
 CONFIG_CMD_MMC=y
 CONFIG_CMD_PART=y