[PowerPC] Move PPCBranchSelector as close to asm printer as possible

Currently, PPCBranchSelector is not immediately preceding asm printer pass. `-debug-pass=Structure` gives
```
      PowerPC Branch Selector
      Contiguously Lay Out Funclets
      StackMap Liveness Analysis
      Live DEBUG_VALUE analysis
      Lazy Machine Block Frequency Analysis
      Machine Optimization Remark Emitter
      Linux PPC Assembly Printer
```
After the patch
```
      Contiguously Lay Out Funclets
      StackMap Liveness Analysis
      Live DEBUG_VALUE analysis
      PowerPC Branch Selector
      Lazy Machine Block Frequency Analysis
      Machine Optimization Remark Emitter
      Linux PPC Assembly Printer
```

Reviewed By: nemanjai, #powerpc

Differential Revision: https://reviews.llvm.org/D104762