Add layer flag to allow creating an effect layer without color fill

This change allows creating an effect layers without a color fill so
we can avoid an additional sf transactions when creating effect
layers.

Fixes: 157646690
Test: go/wm-smoke
Test: atest SurfaceFlinger_test
Change-Id: I3d8a4f4820d7b8fb05daab697c25cff8def612c1