drm_hwcomposer: Tidy-up DrmEncoder class

Implement DrmEncoder instantiation through CreateInstance() static method,
which helps to reduce complexity of DrmDevice::Init() function.

Move Encoder-to-CRTC binding information to the DrmDevice class.

Move drm/DrmEncoder.h to Normal clang-tidy checks list by fixing
clang-tidy findings.

Signed-off-by: Roman Stratiienko <roman.o.stratiienko@globallogic.com>