Fix KMS grab VRAM capture with libva 2.20

[cgutman]

Description

Since libva 2.20, vaInitialize() will fail if we pass a VADisplay backed by a primary node and lack permission to authenticate. Since we don't actually need to have a primary node fd to encode, let's use a render node instead.

Screenshot

Issues Fixed or Closed

Fixes #1690

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Dependency update (updates to dependencies)
• Documentation update (changes to documentation)
• Repository update (changes to repository files, e.g. .github/...)

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated the in code docstring/documentation-blocks for new or existing methods/components

Branch Updates

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Allow edits from maintainers.

• I want maintainers to keep my branch updated