linux: Compile "Intel XHCI USB Role Switch" as a module on x86_64

linux: Compile "Intel XHCI USB Role Switch" as a module on x86_64

From the kernel documentation:

> Driver for the internal USB role switch for switching the USB data
> lines between the xHCI host controller and the dwc3 gadget controller
> found on various Intel SoCs. [...]

This may unblock USB-LAN-adaptor usage on certain boards, as reported
once in #12750. Overall affected devices seem to be scanty;
nevertheless, enabling this as a module only is highly unlikely to cause
any harm, so let's give it a try.

Signed-off-by: Peter Müller <peter.mueller@ipfire.org>