1) Create getBuffer method to return pinned host memory or staging buffer
2) for D2H path use managed buffer instead of static buffer
3) use staging buffer copy for 16KB < size < 1MB
4) use pinned memory copy for size > 1MB
Change-Id: I13d4d6ab60691bc6c7724239db1e11e23f0f3dc2
[ROCm/clr commit: 4bf634dfca]