tilelink2: move general-purpose code out of tilelink2 package

src/main/scala/uncore/tilelink2/Buffer.scala

@@ -4,6 +4,7 @@ package uncore.tilelink2
 
 import Chisel._
 import chisel3.internal.sourceinfo.SourceInfo
+import diplomacy._
 import scala.math.max
 
 // pipe is only used if a queue has depth = 1