This change ports the drm backend to the GraphicsBuffer and
GraphicsBufferAllocator.
The main motivation is to unify graphics buffer abstractions across
various backends and to prepare it for output layers, which could be
nicer if we could have direct control over the buffers.
This makes it possible to ensure type safety for enums, as each drm property
object can have its own type now, and it reduces the amount of typing needed
to access properties
