[llvm] [RISCV] Partially move doPeepholeMaskedRVV into RISCVFoldMasks (PR #72441)

[Luke Lau via llvm-commits]

================
@@ -18,6 +18,7 @@
 
 #include "RISCV.h"
 #include "RISCVSubtarget.h"
+#include "RISCVISelDAGToDAG.h"
----------------
lukel97 wrote:

It's needed for the masked pseudos table, which after everything else is moved over can also be moved into RISCVFoldMasks

https://github.com/llvm/llvm-project/pull/72441