drm_hwcomposer: Rework ValidateDisplay, pushing the layer to plane mapping into Planner

Now we do the z_map creation down in the planner, rework
ValidateDisplay so the layer to plane check we currently
do can be done as part of the initial z_map creation.

There we set the testing_type which will be copied
to the validated_type once validation has completed.

This fixes issues seen preivously where we try to Import
multiple buffers when we only have one plane, and makes
the error paths a bit simpler.

Change-Id: If84e922ba052b35419e7c3d26b821b3400a415b7
Signed-off-by: John Stultz <john.stultz@linaro.org>
1 job for rfc-validate-rework in 36 seconds (queued for 3 seconds)