drm/komeda: Computing layer_split internally

For layer_split no need user to enable/disable it, but compute it in
komeda internally, komeda will enable it if the scaling exceed the
acceptable range of scaler.

Signed-off-by: james qian wang (Arm Technology China) <james.qian.wang@arm.com>
Signed-off-by: Liviu Dudau <Liviu.Dudau@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190708065923.4887-1-james.qian.wang@arm.com