Step1 in staging buffer copy.

- use StagingBuffer class for copies.
- refactor g_device to use array rather than vector.
   (keeps pointers from moving).


[ROCm/hip commit: 24c1fdb864]

projects/hip/util/vim/hip.vim

@@ -151,6 +151,9 @@ syn keyword hipFunctionName hipUnbindTexture
 syn keyword hipFlags hipFilterModePoint 
 syn keyword hipFlags hipMemcpyHostToDevice 
 syn keyword hipFlags hipMemcpyDeviceToHost 
+syn keyword hipFlags hipMemcpyHostToHost 
+syn keyword hipFlags hipMemcpyDeviceToDevice 
+syn keyword hipFlags hipMemcpyDefault 
 syn keyword hipFlags hipReadModeElementType 
 syn keyword hipFlags hipSuccess 
 syn keyword hipFlags hipTextureType1D