Standardize Data.holdUnless and SeqMem.readAndHold

- Make API more idiomatic (x holdUnless y, instead of holdUnless(x, y))
- Add new SeqMem API, readAndHold, which corresponds to most common
  use of holdUnless

src/main/scala/uncore/tilelink2/SRAM.scala

@@ -5,6 +5,7 @@ package uncore.tilelink2
 import Chisel._
 import config._
 import diplomacy._
+import util._
 
 class TLRAM(address: AddressSet, executable: Boolean = true, beatBytes: Int = 4)(implicit p: Parameters) extends LazyModule
 {
@@ -73,7 +74,7 @@ class TLRAM(address: AddressSet, executable: Boolean = true, beatBytes: Int = 4)
       mem.write(memAddress, wdata, in.a.bits.mask.toBools)
     }
     val ren = in.a.fire() && read
-    rdata := holdUnless(mem.read(memAddress, ren), RegNext(ren))
+    rdata := mem.readAndHold(memAddress, ren)
 
     // Tie off unused channels
     in.b.valid := Bool(false)