docs: driver-api: add a series of orphaned documents

There are lots of documents under Documentation/*.txt and a few other
orphan documents elsehwere that belong to the driver-API book.

Move them to their right place.

Reviewed-by: Cornelia Huck <cohuck@redhat.com> # vfio-related parts
Acked-by: Logan Gunthorpe <logang@deltatee.com> # switchtec
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

drivers/vfio/mdev/Kconfig

@@ -6,7 +6,7 @@ config VFIO_MDEV
 	default n
 	help
 	  Provides a framework to virtualize devices.
-	  See Documentation/vfio-mediated-device.txt for more details.
+	  See Documentation/driver-api/vfio-mediated-device.rst for more details.
 
 	  If you don't know what do here, say N.