nds32 patches for 4.20

Here is the nds32 patch set based on 4.20-rc1.
Contained in here are
1. Perf support
2. Power management support
3. FPU support
4. Hardware prefetcher support
5. Build error fixed
6. Performance enhancement

These are the LTP20170427 testing results.
Total Tests: 1902
Total Skipped Tests: 603
Total Failures: 410
Kernel Version: 4.20.0-rc1-00016-ge0db606bc023
Machine Architecture: nds32
Hostname: greentime-d15-ae3xx
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