drm_hwcomposer: Introduce DrmDisplayPipeline class

Create systematic way of binding DRM objects (Crtc,Encoder,Planes...)
to the pipeline using RAII. Use it to create the pipeline.

+ Allow pipeline creation to fail.

Closes: drm-hwcomposer/drm-hwcomposer#14
Signed-off-by: Roman Stratiienko <roman.o.stratiienko@globallogic.com>