RADV Enables Zero vRAM Option For All Games With VKD3D

Mesa's Radeon "RADV" Vulkan driver is now enabling the "zero vRAM" option for all VKD3D games -- Direct3D 12 titles running on Steam Play / Wine with this D3D12 to Vulkan layer -- in order to workaround various rendering bugs.

Doom Eternal (native Vulkan, but still requires this workaround), Metro Exodus, and various other DirectX 12 games that rely on VKD3D when running under Steam Play / Wine have been hitting "colorful graphical aberrations" with the RADV driver but the issues go away when setting RADV_DEBUG=zerovram. As such, that option is now being enabled by default when VKD3D is present.

This option is for zeroing out the video memory to ensure there is no existing/uninitialized data when allocating new RAM for these games.

This commit is now in Mesa 20.2-devel to enable that behavior for all VKD3D usage and is also marked for back-porting to the existing Mesa stable series to fix these graphical glitches.