zink: emulate optional depth-formats

Merged Erik Faye-Lund requested to merge kusma/mesa:zink-depth-format-emu into master

The Vulkan spec says that an implementation has to support one of VK_FORMAT_X8_D24_UNORM_PACK32 and VK_FORMAT_D32_SFLOAT, as well of one of VK_FORMAT_D24_UNORM_S8_UINT and VK_FORMAT_D32_SFLOAT_S8_UINT.

So let's keep track which one is supported of earch pair, and emulate one on top of the other one.

This won't give the exact result for comparisons, or when mapping and unmapping the resources. But it's better than flat out failing to create the resource, and we can fix the map/unmap issue later if needed.

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