[regexp] Port RegExpExecStub to CSA (mostly)

src/mips64/interface-descriptors-mips64.cc

Index: src/mips64/interface-descriptors-mips64.cc
diff --git a/src/mips64/interface-descriptors-mips64.cc b/src/mips64/interface-descriptors-mips64.cc
index 5ce2bb0a4d29fe29b474782273034a5cc1efe26c..62a9918a7633ab30267d6c602d77ab28ea0f94b9 100644
--- a/src/mips64/interface-descriptors-mips64.cc
+++ b/src/mips64/interface-descriptors-mips64.cc
@@ -52,11 +52,15 @@ const Register ApiGetterDescriptor::CallbackRegister() { return a3; }
 
 const Register MathPowTaggedDescriptor::exponent() { return a2; }
 
-
 const Register MathPowIntegerDescriptor::exponent() {
   return MathPowTaggedDescriptor::exponent();
 }
 
+const Register RegExpExecDescriptor::StringRegister() { return a0; }
+const Register RegExpExecDescriptor::LastIndexRegister() { return a1; }
+const Register RegExpExecDescriptor::StringStartRegister() { return a2; }
+const Register RegExpExecDescriptor::StringEndRegister() { return a3; }
+const Register RegExpExecDescriptor::CodeRegister() { return t0; }
 
 const Register GrowArrayElementsDescriptor::ObjectRegister() { return a0; }
 const Register GrowArrayElementsDescriptor::KeyRegister() { return a3; }