[Beignet] [PATCH V4] Enable OpenCL 2.0 only where supported

[Rebecca N. Palmer]

Yang, Rong R wrote:
> Because use -cl-std=CL1.2 by default when OpenCL 2.0 enabled, I prefer to always report address_bits = 32 now.
> OpenCL spec consider only one address bits in one device, but when GEN9 now support both 32 bits and 64 bits address, so there is no way to comply with spec.

As previously noted 
(https://lists.freedesktop.org/archives/beignet/2017-January/008517.html), 
the spec actually says *default* address space size 
(https://www.khronos.org/registry/OpenCL/specs/opencl-2.0.pdf page 64), 
so I agree it should be 32, and device->address_bits 
(src/cl_get_gt_device.h:45) is where this is set.

> An other issue is that beignet OpenCL 2.0 don't support i386 system now, maybe we also need set CAN_OPENCL_20 to off in i386 system.

What happens if you try - explicit error or mystery crash?  Does a 
2.0-capable beignet+hardware work if you only actually use 1.2? 
(Debian's 2.0-enabled beignet does work in an i386 chroot, but that's on 
my non-2.0-capable hardware, and only major bugs are allowed to be fixed 
during freeze.)

> And also need to update readme after this patch merged.

https://sources.debian.net/src/beignet/1.3.0-1/debian/patches/opencl2-runtime-detection.patch/#L351 
is what I used, though you'll want to remove the (Debian-specific) 
jessie-backports reference.

Signed-off-by: Rebecca N. Palmer <rebecca_palmer at zoho.com>