[llvm] [AArch64] When printing SYS aliases, use explicit `NeedsReg` flag from tablegen (NFC) (PR #140484)

[Jack Styles via llvm-commits]

================
@@ -3917,6 +3917,7 @@ bool AArch64AsmParser::parseSysAlias(StringRef Name, SMLoc NameLoc,
   const AsmToken &Tok = getTok();
   StringRef Op = Tok.getString();
   SMLoc S = Tok.getLoc();
+  bool ExpectRegister = true;
----------------
Stylie777 wrote:

I think this should be
```
bool ExpectRegister = false;
```
`NeedsReg` is explicit, and we should only enable it where needed.

https://github.com/llvm/llvm-project/pull/140484