build.yml: Build x86 generic and x1 targets

[henrirosten]

Description of changes

Start building ghaf targets generic-x86_64-debug and lenovo-x1-carbon-gen11-debug in the build.yml workflow. This should work after https://github.com/tiiuae/ghaf/pull/865 since all the builds are now done on the remote builders, not on the github-hosted runners. Earlier attempts to enable generic-x86_64-debug or lenovo-x1-carbon-gen11-debug on the build workflow have failed due to two reasons: (1) github-hosted runners not having enough resources to build these massive targets and (2) hash mismatches I suspect have occurred mostly due to github-hosted runners running the builds on Ubuntu-based VMs. After https://github.com/tiiuae/ghaf/pull/865, both those issues should be resolved by running all the builds on the remote (nix) builders.

Depends-on: https://github.com/tiiuae/ghaf/pull/865: Do not merge before https://github.com/tiiuae/ghaf/pull/865 is merged.

This change was tested in a fork at: https://github.com/henrirosten/ghaf. Especially, see the generic-x86_64-debug and lenovo-x1-carbon-gen11-debug builds on the following test PRs:

• https://github.com/henrirosten/ghaf/pull/68
• https://github.com/henrirosten/ghaf/pull/69
• https://github.com/henrirosten/ghaf/pull/70
• https://github.com/henrirosten/ghaf/pull/71

Checklist for things done

• [x] Summary of the proposed changes in the PR description
• [ ] More detailed description in the commit message(s)
• [x] Commits are squashed into relevant entities - avoid a lot of minimal dev time commits in the PR
• [x] Contribution guidelines followed
• [ ] Ghaf documentation updated with the commit - https://tiiuae.github.io/ghaf/
• [ ] PR linked to architecture documentation and requirement(s) (ticket id)
• [x] Test procedure described (or includes tests). Select one or more:
  • [ ] Tested on Lenovo X1 x86_64
  • [ ] Tested on Jetson Orin NX or AGX aarch64
  • [ ] Tested on Polarfire riscv64
• [x] Author has run make-checks and it passes
• [x] All automatic Github Action checks pass - see actions
• [ ] Author has added reviewers and removed PR draft status
• [ ] Change requires full re-installation
• [ ] Change can be updated with nixos-rebuild ... switch

Instructions for Testing

• [ ] List all targets that this applies to:
• [ ] Is this a new feature
  • [ ] List the test steps to verify:
• [ ] If it is an improvement how does it impact existing functionality?