[PowerPC] Update maintainers (llvm#149171)

Update PowerPC BE maintainers.

Author: RolandF77

llvm/Maintainers.md

@@ -263,6 +263,20 @@ [email protected] (email), [AlexMaclean](https://github.com/AlexMaclean) (GitH
 
 #### PowerPC backend
 
+Amy Kwan (esp. release issues) \
+[email protected] (email), [amy-kwan](https://github.com/amy-kwan) (GitHub) \
+Lei Huang \
+[email protected] (email), [lei137](https://github.com/lei137) (GitHub) \
+Sean Fertile (esp. ABI/ELF/XCOFF) \
+[email protected] (email), [mandlebug](https://github.com/mandlebug) (GitHub) \
+Zhijian Lin \
+[email protected] (email), [diggerlin](https://github.com/diggerlin) (GitHub) \
+Maryam Moghadas \
+[email protected] (email), [maryammo](https://github.com/maryammo) (GitHub) \
+Roland Froese \
+[email protected] (email), [RolandF77](https://github.com/RolandF77) (GitHub) \
+llvmonpower \
+[email protected] (email), [llvmonpower](https://github.com/llvmonpower) (GitHub)
 
 #### RISCV backend