Add Feature to Select Devices to Execute Kernels On

[matinraayai]

It would be great in a multi-device system, the device id that will run a KA kernel could be set through a function call.
cc: @vchuravy

[vchuravy]

We can do this in a backwards compatible manor.

What function do we need?

• device(::Backend)
• device!(::Backend)
• ?devices or ndevices

[matinraayai]

Those, as well as synchronization functions on a single device.
I'll look into CUDA standards to see if there's something else I'm missing.

[vchuravy]

Those, as well as synchronization functions on a single device.

Can you expand on that? We already have synchronize w.r.t to the current active device.

[matinraayai]

Having a synchronize function that takes a device would have been nice, but if there's one w.r.t active device, I think it does the job just as well.

[luraess]

It may also depend if you need stream/queue or device sync. Currently, it implements stream/queue sync for GPU backends.