drm/komeda: Add component komeda_merger

Introduce a new component komeda_merger, because D71 HW supports to split
a whole image to two half parts and does the scaling independently. Merger
merges two separate results to one, and output it to compositor or wb_layer
For this patch:
- Add the definition of komeda_merger/merger_state
- Report and initialize komeda_merger according to the D71 HW.

v2: Rebase

Signed-off-by: James Qian Wang (Arm Technology China) <james.qian.wang@arm.com>
Signed-off-by: Liviu Dudau <liviu.dudau@arm.com>