[ROCm] set parallel=16 when build on ROCm CI (#13368)
### Description
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ROCm CI build step takes more than one hour. Set parallel=16 when build
on ROCm CI to reduce build time.
### Motivation and Context
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- If it fixes an open issue, please link to the issue here. -->
Co-authored-by: peixuanzuo <peixuanzuo@linmif39a000004.zvflicr54joexhdgnhvmxrxygg.phxx.internal.cloudapp.net>
