lavapipe: make ycbcr conformant
The initial ycbcr work didn't support multi-planar formats, but the spec requires that two multi-planar formats are exposed.
This series doesn't some cleanups and fixes, then adds multi-planar support to lavapipe images/image-views/descriptor sets.
It adds support for disjoint images, but turns off midpoint chroma as it fails some tests.
dEQP-VK.ycbcr.* has no fails with this.