mantle/gcp: Only set x86-specific guest OS features on x86_64 images

[dustymabe]

ARM GCP images were being created with x86-specific confidential computing guest OS features (SEV_CAPABLE, SEV_SNP_CAPABLE, TDX_CAPABLE) that are not applicable to the ARM64 platform. Move these features along with SEV_LIVE_MIGRATABLE_V2 into the x86_64-specific branch so ARM64 images only get the architecture-independent features: VIRTIO_SCSI_MULTIQUEUE, GVNIC, UEFI_COMPATIBLE, and IDPF.

Fixes: coreos/fedora-coreos-tracker#2106

Written-by: <anthropic/claude-opus-4.6>

[openshift-ci]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
You can still manually trigger a test run with /test all

[gemini-code-assist]

Code Review

This pull request refactors the GCP image creation logic to consolidate architecture-specific features. The review identified that a TODO comment regarding SEV_CAPABLE was inadvertently removed during the refactoring, and suggested restoring it along with the original descriptive comments to maintain context and readability.

[travier]

Not tested (sight) but LGTM

[aaradhak]

Verification:

1. Downloaded test images:
   ```
   - fedora-coreos-43.20260331.2.1-gcp.x86_64.tar.gz
   - fedora-coreos-43.20260331.2.1-gcp.aarch64.tar.gz

  2. Uploaded tarballs to GCS:

gcloud storage cp fedora-coreos-43.20260331.2.1-gcp.x86_64.tar.gz gs://rhcos-devel/test-gcp-fix-x86-64.tar.gz --project=openshift-rhcos-devel
gcloud storage cp fedora-coreos-43.20260331.2.1-gcp.aarch64.tar.gz gs://rhcos-devel/test-gcp-fix-aarch64.tar.gz --project=openshift-rhcos-devel

 3. Created images with the features the patched ore code would set:
  # x86_64 :

gcloud compute images create test-gcp-fix-x86-64
--project=openshift-rhcos-devel
--source-uri=gs://rhcos-devel/test-gcp-fix-x86-64.tar.gz
--architecture=X86_64
--guest-os-features=VIRTIO_SCSI_MULTIQUEUE,GVNIC,UEFI_COMPATIBLE,IDPF,SEV_CAPABLE,SEV_SNP_CAPABLE,TDX_CAPABLE,SEV_LIVE_MIGRATABLE_V2

  # aarch64 - only common features, no SEV/TDX

gcloud compute images create test-gcp-fix-aarch64
--project=openshift-rhcos-devel
--source-uri=gs://rhcos-devel/test-gcp-fix-aarch64.tar.gz
--architecture=ARM64
--guest-os-features=VIRTIO_SCSI_MULTIQUEUE,GVNIC,UEFI_COMPATIBLE,IDPF

  4. Verified features:

$ gcloud compute images describe test-gcp-fix-x86-64 --project=openshift-rhcos-devel --format="table(guestOsFeatures.type:label=FEATURE)"
FEATURE
['VIRTIO_SCSI_MULTIQUEUE', 'GVNIC', 'UEFI_COMPATIBLE', 'IDPF', 'SEV_CAPABLE', 'SEV_SNP_CAPABLE', 'TDX_CAPABLE', 'SEV_LIVE_MIGRATABLE_V2']

$ gcloud compute images describe test-gcp-fix-aarch64 --project=openshift-rhcos-devel --format="table(guestOsFeatures.type:label=FEATURE)"
FEATURE
['VIRTIO_SCSI_MULTIQUEUE', 'GVNIC', 'UEFI_COMPATIBLE', 'IDPF']

  Result: x86_64 includes all 8 features (SEV_CAPABLE, SEV_SNP_CAPABLE, TDX_CAPABLE, SEV_LIVE_MIGRATABLE_V2) while aarch64 correctly has only the 4 common features with no confidential computing features.