uio: Documentation: Add information on using uio_pdrv_genirq with DT

Add a paragraph to describe the use of the "of_id" module parameter,
along with the new DT property.

Signed-off-by: Daniel Mack <daniel@zonque.org>
Link: https://lore.kernel.org/r/20190815212807.25058-2-daniel@zonque.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>