platforms/drm: support Broadcast_RGB setting
This allows the user to switch between full and limited rgb with the Broadcast_RGB drm property. This is currently supported by Intel but support for others, mainly AMD, is being worked on: https://gitlab.freedesktop.org/drm/amd/-/issues/476
Depends on kwayland-server!282 (merged) and libraries/plasma-wayland-protocols!20 (merged). For testing you'll also want https://invent.kde.org/frameworks/kwayland/-/merge_requests/44, libkscreen!30 (merged) and kscreen!39 (merged)