Support multi-GPU/hybrid systems in auto-detection

[ericbsd]

Problem Statement

The xconfig auto command only configures the first detected GPU, which causes issues on hybrid/multi-GPU systems (common in modern laptops with integrated + discrete graphics).

Current Behavior

Detection order in cmd_auto():

1. Intel GPU → configures Intel DRM
2. AMD GPU → configures AMD DRM
3. NVIDIA GPU → configures NVIDIA

Impact: On hybrid laptops (e.g., Intel iGPU + NVIDIA dGPU), only the Intel GPU gets configured. The discrete GPU remains unused.

Expected Behavior

• Detect all available GPUs
• Configure the system appropriately for hybrid/multi-GPU setups
• Provide user control over GPU selection when needed

Technical Details

File: bin/xconfig
Function: cmd_auto() (lines 743-809)

Detection functions:

• detect_intel_gpu()
• detect_amd_gpu()
• detect_nvidia_gpu()

Currently use return 0 on first match, stopping further detection.

Tasks

Investigation Phase

• Research FreeBSD best practices for hybrid GPU configurations
• Investigate how other BSD tools handle multi-GPU systems
• Determine if both GPUs can/should be configured simultaneously
• Document findings and recommend approach

Implementation Phase

• Enumerate all GPUs instead of early return
• Implement chosen approach from investigation
• Add GPU priority logic or user selection menu
• Log all detected GPUs for debugging
• Update documentation with multi-GPU behavior

Testing Phase

• Test on hybrid laptop (Intel + NVIDIA)
• Test on hybrid laptop (Intel + AMD)
• Test on desktop with multiple GPUs
• Test on single GPU systems (ensure no regression)