drm/komeda: Add new component komeda_splitter

Similar to Layer Split, but Splitter is used for writeback, which splits
the compiz result to two half parts and then feed them to two scalers.

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>