config: use Field defaults over Config defaults

Also rename some keys that had the same class name as their value's class name.

src/main/scala/tilelink/Bus.scala

@@ -6,7 +6,7 @@ import Chisel._
 import freechips.rocketchip.config.{Field, Parameters}
 import freechips.rocketchip.diplomacy._
 
-case object TLBusDelayProbability extends Field[Double]
+case object TLBusDelayProbability extends Field[Double](0.0)
 
 /** Specifies widths of various attachement points in the SoC */
 trait TLBusParams {