Documentation/EDAC: Fix warning document isn't included in any toctree

Fix the build (htmldocs) warning:

  Documentation/edac/index.rst: WARNING: document isn't included in any toctree.

Fixes: db99ea5f ("EDAC: Add support for EDAC device features control")
Closes: https://lore.kernel.org/all/20250228185102.15842f8b@canb.auug.org.au/


Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Shiju Jose <shiju.jose@huawei.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20250401115823.573-1-shiju.jose@huawei.com