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>
diff --git a/drivers/dma-buf/Kconfig b/drivers/dma-buf/Kconfig
index d5f9158..b6a9c2f 100644
--- a/drivers/dma-buf/Kconfig
+++ b/drivers/dma-buf/Kconfig
@@ -15,7 +15,7 @@
 	  associated with a buffer. When a job is submitted to the GPU a fence
 	  is attached to the buffer and is transferred via userspace, using Sync
 	  Files fds, to the DRM driver for example. More details at
-	  Documentation/sync_file.txt.
+	  Documentation/driver-api/sync_file.rst.
 
 config SW_SYNC
 	bool "Sync File Validation Framework"