SVM buffer address equivalence tests

[bashbaug]

Here are some tests to check how SVM pointers on the host relate to pointer values on the device when a buffer memory object is created from the SVM pointer. See:

• Creating Memory Objects from Offset SVM Pointers OpenCL-Docs#1369
• Memory Consistency for Memory Objects Created from SVM Allocations OpenCL-Docs#1370

Some other interesting tests might be:

• Create a buffer from a pointer offset into the SVM allocation, rather than the base of the SVM allocation
• Create a sub-buffer from the buffer created from the SVM pointer