Before this change, we simply fail if the device does not expose one
queue family that supports both graphics and present. Currently this is
fine, since devices tend to lay out their queues in this way. NV, for
instance, tends to have one queue family for all graphics operations and
one more for transfer only. However, it's not a hard requirement, and it
is cheap to use a separate queue, so we might as well.
This stops the virtual method call from within the Renderer constructor.
The initialization here for GL had to be moved to VideoBackend, as the
Renderer constructor will not have been executed before the value is
required.
Hopefully will fix the crash in vkDestroyInstance on the NV Shield TV,
and likely reduce boot times slightly for drivers that take a while
to create instances.
