d3d11memory: Always use native DXGI format if device support it

d3d11memory: Always use native DXGI format if device support it

Use consistent memory layout between dxva and other shader use case.
For example, use DXGI_FORMAT_NV12 texture format instead of
two textures with DXGI_FORMAT_R8_UNORM and DXGI_FORMAT_R8G8_UNORM.