Add vkEnumeratePhysicalDeviceGroupsKHR() (and related bindings)

[awr1]

https://www.khronos.org/registry/vulkan/specs/1.0-extensions/html/vkspec.html#_device_group_queries

These bindings would enable multi-physical GPU support within a single logical GPU.

[gmpreussner]

Thanks awr1, I won't have time to work on this anytime soon. If you wanna send a pull request, that would be awesome though.