The goal of this merge request is to allow radeonsi's VA-API driver to produce NV12 buffers that can be scanned out by KMS on a rotated hw plane. amdgpu requires buffers to have a tiled (ie, non-linear) layout for rotated hw planes. This MR can be tested together with an amdgpu patch.
The first part of this MR adds support for VASurfaceAttribDRMFormatModifiers, a new VA-API surface attribute that allows applications to choose the format modifier picked by the driver for buffer allocations. The second part of this MR enables non-linear multi-planar buffers for all of the Mesa AMD drivers.