docs: kernel-parameters.txt: document xhci-hcd.quirks parameter

This parameter introduced several years ago in the XHCI host controller
driver was somehow left undocumented. Add a few lines in the kernel
parameters text.

Signed-off-by: Laurentiu Tudor <laurentiu.tudor@nxp.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>