At present this driver is always included in SPL and TPL, if U-Boot proper enables it. Update the Makefile to provide full control using the existing Kconfig options. Signed-off-by: Simon Glass <sjg@chromium.org> Reviewed-by: Bin Meng <bmeng.cn@gmail.com> [bmeng: make the Kconfig help text a little bit clearer] Signed-off-by: Bin Meng <bmeng.cn@gmail.com>