rocFFT 1.0.15 for ROCm 5.0.0

Changed

• Re-aligned split device library into 4 roughly equal libraries.
• Implemented the FuseShim framework to replace the original OptimizePlan
• Implemented the generic buffer-assignment framework. The buffer assignment
  is no longer performed by each node. We designed a generic algorithm to
  test and pick the best assignment path.
  With the help of FuseShim, we can achieve more kernel-fusions as possible.
• Do not read the imaginary part of the DC and Nyquist modes for even-length
  complex-to-real transforms.

Optimizations

• Optimized twiddle-conjugation; complex-to-complex inverse transforms should have similar performance to foward transforms now.
• Improved performance of single-kernel small 2D transforms.