Wayland screencast: refactor EGL DMA-BUF handling for multi-GPU support

Refactor EGL DMA-BUF implementation to support multi-GPU systems.

Key changes:
- Split into EglDrmDevice (per-device state) and EglDmaBuf (device
  manager)
- Enumerate all EGL devices using eglQueryDevicesEXT
- Use lazy initialization to avoid waking GPUs in low-power states
- Prefer Wayland platform device, fall back to first enumerated device

Bug: webrtc:461543454
Change-Id: Ief0ebabd6067df4f1e18d11eed01c61644e0231a
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/427363
Reviewed-by: Alexander Cooper <alcooper@chromium.org>
Commit-Queue: Jan Grulich <grulja@gmail.com>
Cr-Commit-Position: refs/heads/main@{#46556}