[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