[Beignet] [PATCH newRT] Add cl_gen_device_common.h file.

[Rebecca N. Palmer]

> I think a better choice is to make OpenCL 1.2 also use 64bit address. So that we have a unified address_bits across 1.2 and 2.0.
> But using 64bit address would hurt some performance. I think we need more work on 64bit optimization to make "unified address_bits across different ocl version" affect as less as we can.

Will that break older hardware (no emitUntypedReadA64Instruction) like 
unconditionally enabling OpenCL 2.0 does, or is this only intended to 
apply to 2.0-capable hardware?