Unlike the other drivers, the D3D12 driver is hardware accelerated, so
it's going to be a more reasonable choice. So let's prefer it.
This only matters for people who build with the D3D12 driver. And they
can set the GALLIUM_DRIVER environment variable as appropriate to
override it.
Reviewed-by: Jesse Natalie <jenatali@microsoft.com>
Acked-by: Adam Jackson <ajax@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7534>