Clarify what devices are selected by `clCreateContextFromType`

[kpet]

Currently specified as follows

To create an OpenCL context from a specific device type, call clCreateContextFromType Only devices that are returned by clGetDeviceIDs for device_type are used to create the context. The context does not reference any sub-devices that may have been created from these devices.

A few things to consider (from discussion in 2025/06/17 teleconference)

• What is the behaviour when passing CL_DEVICE_TYPE_ALL
• Should the description refer to "all devices that are returned" instead of "only devices that are returned"
• Some reported that the conformance tests did not match the specification. We should make sure they are aligned.
• Anything else?