v3dv: drm format modifier fixes
We can't expose VK_EXT_image_drm_format_modifier yet (it depends on VK_KHR_sampler_ycbcr_conversion), but we had a partial implementation because the Vulkan WSI implementation relies on some of this functionality. This MR adds a couple of small things that were missing.
With these changes, if we expose VK_EXT_image_drm_format_modifier and work around a limitation in the current CTS test coverage, we pass all the tests we support under dEQP-VK.drm_format_modifiers.