anv: add VK_EXT_physical_device_drm
WIP until the extension is merged in the Vulkan repository : https://github.com/KhronosGroup/Vulkan-Docs/pull/1356
Edited by Lionel Landwerlin
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WIP until the extension is merged in the Vulkan repository : https://github.com/KhronosGroup/Vulkan-Docs/pull/1356