Peer-to-Peer improvements.

- Bug fix for peer visibility.  Now contexts correctly detect when they can use SDMA for P2P vs staging buffers.
- Interface to new HCC copy_ext function.
- Improve context and peer print /debug options.
- Add comments and usage to hipPeerToPeer_simple test.


[ROCm/hip commit: c769abcbeb]

projects/hip/src/hip_memory.cpp

@@ -104,7 +104,7 @@ hipError_t hipMalloc(void** ptr, size_t sizeBytes)
     if (sizeBytes == 0)
     {
         *ptr = NULL;
-        return ihipLogStatus(hip_status);
+        return ihipLogStatus(hipSuccess);
     }
    
     auto ctx = ihipGetTlsDefaultCtx();