linux6.11: Enable dm-vdo compression/deduplication module.

[klardotsh]

For context on what VDO is, see the userspace utilities repo README or this Red Hat blog post.

Testing the changes

• I tested the changes in this PR: briefly

"Tested" in the sense of:

• I built locally for x86_64 and aarch64 (glibc)
• During builds, I verified that Kconfig stated no changes to the config file were to be applied
• After installing the package, I verified that the kernel module existed on disk in a reasonable location:

$ file /lib/modules/6.11.6_2/kernel/drivers/md/dm-vdo/dm-vdo.ko.zst
/lib/modules/6.11.6_2/kernel/drivers/md/dm-vdo/dm-vdo.ko.zst: Zstandard compressed data (v0.8+), Dictionary ID: None

Doing further testing of this requires userspace utilities I have yet to package (but hopefully intend to later today/this weekend)

I intend to open separate PRs to do a similar enablement for linux6.10 and linux6.9. (VDO was only upstreamed starting in 6.9. EDIT: we don't package 6.9 anyway, cool).

[github-actions]

Pull Requests become stale 90 days after last activity and are closed 14 days after that. If this pull request is still relevant bump it or assign it.

[klardotsh]

This got no traction or reviews, and I wound up back on ZFS anyway rather than trying to fight an all dm-* stack, so closing. Anyone is free to revive this work if they're interested in it, of course!