docs: media: Allow creating cross-references for RC ABI

Now that Documentation/ABI is processed by automarkup, let it
generate cross-references for RC sysfs devnodes.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/7c2f9a9970a15df8b5e3a6ecd21bcedcc8881ce1.1739254867.git.mchehab+huawei@kernel.org