rephrase and correct the descriptions for clSetKernelExecInfo

[bashbaug]

fixes #1152
fixes #1244

Rephrases and corrects the descriptions for multiple parts of clSetKernelExecInfo.

Removes the cumbersome "note" below the API description and moves the content into the API description instead. I don't think I lost any important content, but this would be a good area for a careful review.

Explicitly states that an empty set of SVM pointers for CL_KERNEL_EXEC_INFO_SVM_PTRS is valid.

[bashbaug]

Depending how we resolve #1244 we may need to make additional clarifications.

[bashbaug]

Converting to draft to work out system SVM updates.

[bashbaug]

This is ready for review again.

[karolherbst]

I'm not sure if the CL_KERNEL_EXEC_INFO_SVM_FINE_GRAIN_SYSTEM part is really needed here. A client could use a kernel on multiple devices, some not supporting system SVM. Should we now require applications to flip CL_KERNEL_EXEC_INFO_SVM_FINE_GRAIN_SYSTEM each time they enqueue the kernel on a different device?

It kinda feels more like an inconvenience, because for the runtime it's more or less meaningless as well. If an application uses a system SVM pointer on a device not supporting it indirectly, having CL_KERNEL_EXEC_INFO_SVM_FINE_GRAIN_SYSTEM set to CL_TRUE or CL_FALSE doesn't really change anything about the abnormal behavior the client will see.

There is another aspect to this, by default CL_KERNEL_EXEC_INFO_SVM_FINE_GRAIN_SYSTEM is CL_TRUE/CL_FALSE depending on the device. An application might set it to CL_FALSE for devices supporting system SVM to be nice to the runtime, but maybe they want to revert that, so now they'll need to toggle, which earlier they probably wouldn't had to.

I think it would probably make more sense to simply state, that CL_KERNEL_EXEC_INFO_SVM_FINE_GRAIN_SYSTEM is assumed to be always CL_FALSE on devices the kernel gets enqueued not supporting system SVM or that this flag only has an impact on kernels for devices supporting system SVM.

Though to be fair, I doubt there is any applications doing that, but so far it just sounds like an inconvenience gets added for no real benefit.

[bashbaug]

Full disclosure: I've never liked CL_KERNEL_EXEC_INFO_SVM_FINE_GRAIN_SYSTEM. Having the default state dependent on the capabilities of the device always seemed especially problematic.

This is an interesting idea:

I think it would probably make more sense to simply state, that CL_KERNEL_EXEC_INFO_SVM_FINE_GRAIN_SYSTEM is assumed to be always CL_FALSE on devices the kernel gets enqueued not supporting system SVM or that this flag only has an impact on kernels for devices supporting system SVM.

I think this could solve the default state problem as well, since then the default could be CL_TRUE if any device supports system SVM, and it'd just be ignored for devices that do not support system SVM.

If we're OK with this, I think I'd just need to make a few small edits to remove this error condition and to tidy up the CL_KERNEL_EXEC_INFO_SVM_FINE_GRAIN_SYSTEM description.