media: v4l2-fwnode: Add a deprecation note in the old ACPI parsing example

This is not how ACPI tables are written. Add a deprecation note and refer
to the proper documentation.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>