uboot-imx

configs: Remove CONFIG_SYS_USB_XHCI_MAX_ROOT_PORTS in all boards

Now that xHCD does not use CONFIG_SYS_USB_XHCI_MAX_ROOT_PORTS,
remove it in all boards' config files.

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>