Move kmod-6.18 nvidia drivers to use overlayfs at boot

[vigh-m]

Description of changes:
Enables the NVIDIA lts (r580) and fb (r595) driver branches to be co-installed on a single Bottlerocket image, with exactly one branch activated at boot. Single-driver images continue to work unchanged.

Both branches previously installed their libraries, binaries, module objects and configs directly onto the canonical system paths (/usr/lib64, /usr/bin, /usr/share/nvidia, /etc/nvidia, ...). This PR moves each branch's files under a per-branch storage root and overlays the selected branch onto the canonical paths at boot.

• Each branch installs into /usr/nvidia/<branch>/ (lts or fb).
• Per-branch, oneshot services mount overlays that make the storage root's contents appear at the canonical paths:
  • nvidia-<branch>-overlay-driver.service: lib64, bin, share-nvidia, share-vulkan, share-glvnd, share-egl.
  • nvidia-<branch>-overlay-config.service: etc-nvidia -> /etc/nvidia, etc-nvidia-imex -> /etc/nvidia-imex.
• The /usr/lib64 overlay would otherwise shadow the writable /usr/lib/modules mount, so the base module tree is bound to a /run mount point and re-layered as a lowerdir with a writable upper under /var/lib/kernel-modules/.nvidia.
• driverdog link/load/copy unit filenames are namespaced per branch (nvidia-lts-* / nvidia-fb-*) so both branches' units coexist without collision. driverdog config tomls are also branch-named and installed normally into the flat /etc/drivers.

New driver file layout

Each branch now lives under its own root, e.g.:

  [root@admin]# tree /.bottlerocket/rootfs/usr/nvidia/ -d
  /.bottlerocket/rootfs/usr/nvidia/
  `-- fb
      |-- bin
      |-- etc-nvidia
      |-- etc-nvidia-imex
      |-- lib64
      |   `-- tesla
      |-- share-egl
      |   `-- egl_external_platform.d
      |-- share-glvnd
      |   `-- egl_vendor.d
      |-- share-nvidia
      |   |-- grid
      |   |   `-- drivers
      |   |-- open-gpu
      |   |   `-- drivers
      |   `-- tesla
      |       |-- module-objects.d
      |       `-- nvswitch
      `-- share-vulkan
          |-- icd.d
          `-- implicit_layer.d

Renames

To keep the projected roots unambiguous under the storage root, the
packaged trees were renamed:

Before	After	Overlayed onto
share/	share-nvidia/	/usr/share/nvidia
etc/ (nvidia)	etc-nvidia/	/etc/nvidia
etc/ (imex)	etc-nvidia-imex/	/etc/nvidia-imex

Backwards compatibility

• A single-driver image installs exactly one branch; its overlay services project that branch onto the canonical paths, giving the same runtime layout as before.
• co-install guard: add a Provides and a Conflicts that guards lts+fb co-install unless kmod-nvidia-multi is present. This is to prevent any attempts to install both drivers without the right logic to pick the right driver at boot

Testing

• Single-driver lts (r580) image: boots, driver loads, nvidia-smi works
• Single-driver fb (r595) image: boots, driver loads, nvidia-smi works
• Overlay mounts present after boot (lib64/bin/share-nvidia/etc-nvidia)
• Nvidia Smoke test workload on g4dn, g5, g6, g7(595 only)
• MIG and EFA testing (580 and 595)

Terms of contribution:

By submitting this pull request, I agree that this contribution is dual-licensed under the terms of both the Apache License, version 2.0, and the MIT license.