Vec considered harmful; use isOneOf instead (#64)

Vec is heavyweight and really should only be used for I/O and
dynamic indexing.  A recurring pattern in uncore is

    Vec(const1, const2, const3) contains x

which is nice but has a deleterious effect on simulation copilation
and execution time.  This patch proposes an alternative:

    x isOneOf (const1, const2, const3)
    x isOneOf seqOfThings

I think it's also more idiomatic.

This is just a prototype; I'm not wed to the name or implementation.

uncore/src/main/scala/agents/Broadcast.scala

@@ -6,6 +6,7 @@ import Chisel._
 import uncore.coherence._
 import uncore.tilelink._
 import uncore.constants._
+import uncore.Util._
 import cde.Parameters
 
 class L2BroadcastHub(implicit p: Parameters) extends HierarchicalCoherenceAgent()(p) {
@@ -155,7 +156,7 @@ class BufferedBroadcastAcquireTracker(trackerId: Int)(implicit p: Parameters)
   // and/or write back dirty data, and may be unexpected voluntary releases
   def irel_can_merge = io.irel().conflicts(xact_addr_block) &&
                          io.irel().isVoluntary() &&
-                         !Vec(s_idle, s_meta_write).contains(state) &&
+                         !state.isOneOf(s_idle, s_meta_write) &&
                          !all_pending_done &&
                          !io.outer.grant.fire() &&
                          !io.inner.grant.fire() &&