Start calling DrmHwcTwo.{cpp,h} - Frontend

Limit responsibility of HWC2 frontend:
1. Deliver information from/to client and convert between android/internal
   data types.
2. Use internal API to communicate with displays/compositors. Remove any
   composition logic from frontend module. (out of scope)
3. Minimize ModeList logic in frontend. (out of scope)

Define Internal Data Types:
- Internal data types should be minimalistic and suffitient to compose
using DRM API and V4L2 in the future.
- Use 'Internal' prefix instead of 'DrmHwc' to make code hacking easier.

Signed-off-by: Roman Stratiienko <r.stratiienko@gmail.com>