Development/monitor modes fixes

[bramoosterhuis]

Fix DRM Pipeline Initialization for Platforms Without Pre-configured Encoders

Problem

On some platforms (e.g., BananaPi with Allwinner H3), the DRM driver does not pre-configure the encoder pipeline. The existing code assumed connector->encoder_id would always be set, causing initialization failures when starting from a cold boot state.

Changes

1. Enhanced Encoder Selection (DRM.cpp)

• Strategy 1: Use pre-assigned encoder if connector->encoder_id is valid
• Strategy 2: Search through connector's compatible encoders when no encoder is assigned
  • Prefer encoders already associated with a CRTC (warm state)
  • Fall back to free encoders
  • Validate encoder compatibility via possible_crtcs bitmask

2. CRTC Allocation

• Allocate CRTC from possibleCrtcs bitmask when encoder has no CRTC assigned
• Pick first available CRTC that matches the bitmask

3. Primary Plane Discovery

• Fixed plane search to find PRIMARY planes compatible with selected CRTC
• Check plane->possible_crtcs bitmask against CRTC index
• Support both warm boot (plane already active) and cold boot (find unused PRIMARY plane)

4. Logging Improvements

• Fixed division-by-zero when CRTC has no active mode (cold boot)
• Added comprehensive trace logging for encoder/CRTC/plane selection process
• Clear indication of warm vs cold boot paths

5. DRM Identifier Consistency

• Changed DRM::InvalidIdentifier from ~0 to 0 to match kernel convention
• All DRM objects (encoders, CRTCs, planes) use 0 as invalid ID

Testing

Tested on BananaPi M2 with Allwinner H3 SoC:

• ✅ Cold boot initialization (no pre-configured pipeline)
• ✅ Encoder search and selection
• ✅ CRTC allocation from possibleCrtcs bitmask
• ✅ Primary plane discovery
• ✅ Proper modeset marking for inactive displays

Impact

• Fixes compositor initialization on platforms where DRM driver leaves encoder pipeline unconfigured
• Maintains backward compatibility with platforms that pre-configure encoders
• More robust handling of cold boot scenarios