[LLVM] Update SelectionDAG maintainers (llvm#116408)

bogner is listed as the current SDAG maintainer, but mostly works on
DirectX nowadays and isn't directly involved with SDAG work anymore.

Add RKSimon and topperc as new SelectionDAG maintainers.

Author: nikic

llvm/Maintainers.md

@@ -121,8 +121,10 @@ [email protected] (email)
 
 #### SelectionDAG
 
-Justin Bogner \
-[email protected] (email), [bogner](https://github.com/bogner) (GitHub)
+Simon Pilgrim \
+[email protected] (email), [RKSimon](https://github.com/RKSimon) (GitHub) \
+Craig Topper \
+[email protected] (email), [topperc](https://github.com/topperc) (GitHub)
 
 #### FastISel
 
@@ -462,6 +464,7 @@ [email protected] (email), [lattner](https://github.com/lattner) (GitHub), clattn
 ### Inactive or former component maintainers
 
 Hans Wennborg ([email protected], [zmodem](https://github.com/zmodem)) -- Release management
+Justin Bogner ([email protected], [bogner](https://github.com/bogner)) -- SelectionDAG
 
 ### Former maintainers of removed components