[mips] Move the setATReg definition inside the MipsAssemblerOptions class. NFC.

[tomatabacu]

Summary

This groups all of the MipsAssemblerOptions functionality together, making it more reader-friendly.

[dsanders]

LGTM

lib/Target/Mips/AsmParser/MipsAsmParser.cpp

public:
   MipsAssemblerOptions(const MipsAssemblerOptions *Opts) {
     ATReg = Opts->getATRegNum();
     Reorder = Opts->isReorder();
     Macro = Opts->isMacro();
     Features = Opts->getFeatures();
   }
 
   unsigned getATRegNum() const { return ATReg; }
-  bool setATReg(unsigned Reg);
+  bool setATReg(unsigned Reg) {
+    if (Reg > 31)
+      return false;
+
+    ATReg = Reg;
+    return true;
+  }
 
   bool isReorder() const { return Reorder; }
   void setReorder() { Reorder = true; }
   void setNoReorder() { Reorder = false; }
 
   bool isMacro() const { return Macro; }
   void setMacro() { Macro = true; }
   void setNoMacro() { Macro = false; }
CC = StringSwitch<unsigned>(Name)
            .Case("msarequest", 5)
            .Case("msamap", 6)
            .Case("msaunmap", 7)
            .Default(-1);
 
   return CC;
 }
 
-bool MipsAssemblerOptions::setATReg(unsigned Reg) {
-  if (Reg > 31)
-    return false;
-
-  ATReg = Reg;
-  return true;
-}
-
 int MipsAsmParser::getATReg(SMLoc Loc) {
   int AT = AssemblerOptions.back()->getATRegNum();
   if (AT == 0)
     reportParseError(Loc,
                      "pseudo-instruction requires $at, which is not available");
   return AT;
 }