uboot-imx

Kconfig: Drop CONFIG_CMD_TFTP

This is not a valid CONFIG option. Drop it.

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>