Introduce a utility function for integer division with rounding up

See https://github.com/KhronosGroup/OpenCL-CTS/pull/2105

We should consider a utility to round up to a multiple of a number too. This is also commonly used.

Start by reviewing pull request 2105 and searching the OpenCL-CTS codebase for existing integer-division or round-up helpers. Determine the intended utility API and whether rounding to a multiple belongs in the same change; done means the utility is available to relevant tests with coverage for integer division rounded up and the proposed multiple-rounding case.

Written by the indexing model from the issue text.