This is a standard compare and swap but implemented on vector memory
buffer instructions (i.e., it is the same as FLAT_ATOMIC_CMPSWAP with
MUBUF's special address calculation).
This was tested using a Tensile kernel, a backend for rocBLAS, which is
used by PyTorch and Tensorflow. Prior to this patch both ML frameworks
crashed. With this patch they both make forward progress.
Change-Id: Ie76447a72d210f81624e01e1fa374e41c2c21e06
4d336c0636