Revert "cmd/internal/obj/loong64: use the MOVVP instruction to optimize prologue"

This reverts commit eb7c67f.

Reason for revert: Causes x/tools/gopls/internal/filecache/TestConcurrency failures, See issue 75571.

Fixes golang#75571
Fixes golang#75572

Change-Id: Ife328dce917c63c872da35f4a9e9f7ef8f88c712
Reviewed-on: https://go-review.googlesource.com/c/go/+/706035
Reviewed-by: Michael Pratt <[email protected]>
Auto-Submit: Michael Pratt <[email protected]>
Reviewed-by: Junyang Shao <[email protected]>
Reviewed-by: sophie zhao <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Meidan Li <[email protected]>

Author: abner-chenc

src/cmd/internal/obj/loong64/obj.go

@@ -324,7 +324,7 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 				q = c.ctxt.StartUnsafePoint(q, c.newprog)
 
 				q = obj.Appendp(q, newprog)
-				q.As = AMOVVP
+				q.As = mov
 				q.Pos = p.Pos
 				q.From.Type = obj.TYPE_REG
 				q.From.Reg = REGLINK