linux-imx

docs: Use reference to link to rst file

Current document includes the path to an RST doc file.  Since this is an
RST file we can make this a link.  Keeps the path as the link title
since that what the original author wrote.

Use reference to link to rst file.

Signed-off-by: Tobin C. Harding <tobin@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>