drm/komeda: Add layer split support

Komeda supports two types of layer split:
- none-scaling split
- scaling split
Since D71 merger only support scaler as input, so for none-scaling split,
the two layer dflow will be output to compiz directly. for scaling_split,
the data flow will be merged by merger firstly, then output the merged
data flow to compiz.

Komeda handles the split in kernel completely to hide the detailed and
complicated split calcualtion to user mode, for user only need to set the
layer_split property to enable/disable it.

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>