drm_hwcomposer: always put protected layers on hardware planes

Protected layers will not work inside of the GLWorker, so we are forced to put
them into planes directly.

Because we can now receive display contents which can never be properly
composited (e.g. 4 protected layers on hardware with only 3 planes), some
compromises had to be made for the composition planning algorithm. First all
protected layers are given a plane. Then the remaining planes are used by the
remaining layers, pre-composite buffer, and squash buffer. In the case where
there are too few planes for both a pre-composite buffer and squash buffer,
everything gets pushed into the pre-composite buffer and the squash buffer
will not be composited onto the screen. Another major limitation is that any
unprotected layers appearing behind a protected layer will actually appear on
top of that protected layer.

TEST=run protected content with lots of other layers

Change-Id: I94620d93f68ca14dc1966422dc89035ab84e3ff4
5 files changed