CL adapter improvement: enable USM hints

[aarongreig]

We have big commented out blocks in our implementations of USMAdvise and USMPrefetch

unified-runtime/source/adapters/opencl/usm.cpp

Line 377 in 9390279

/*

suggesting that the CL equivalents to these functions aren't yet widely supported. I had a go at uncommenting one of these and fixing the mild bitrot that's set in, and at the very least I didn't get an error when I tested it (on gen 12 igpu driver). We should look at removing the comments if support has indeed been rolled out to a decent extent.

[aarongreig]

looks like this will be addressed by the changes in #2312