Fix hsaKmtRegisterMemory to be a no-op for now and move the multi-GPU
implementation to hsaKmtRegisterMemoryToNodes. Make GPU memory mappings
of host memory visible to all GPUs by default. Device memory is still
visible to the allocating GPU only by default (but can be overridden
with hsaKmtRegisterMemoryToNodes for experimenting with P2P).
Change-Id: I73408afbe3b10c8dad2ab3a780f58413249692e6
Felix Kuehling
Flora Cui
Oded Gabbay
Xihan Zhang