As all x86 boards have been switched over to use DM USB, remove
CONFIG_USB_MAX_CONTROLLER_COUNT which is not used by DM USB.
Signed-off-by: Bin Meng <bmeng.cn@gmail.com> Reviewed-by: Simon Glass <sjg@chromium.org> Reviewed-by: Stefan Roese <sr@denx.de> Tested-by: Stefan Roese <sr@denx.de>