[Unity] NDArray Cache Efficient Load in OpenCL

[MasterJH5574]

OpenCL runtime may allocate mirror memory
for device memory that serves as host copy target.

This PR uses a staging buffer for parameter load
to avoid this problem.

Authored by Tianqi.

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Co-authored-by: Tianqi Chen tqchenml@gmail.com

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• cc @quic-sanirudh _{See #10317 for details}

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