Param: Transition to Cycles for relevant parameters

This patch is a first step to using Cycles as a parameter type. The
main affected modules are the CPUs and the Ruby caches. There are
definitely plenty more places that are affected, but this patch serves
as a starting point to making the transition.

An important part of this patch is to actually enable parameters to be
specified as Param.Cycles which involves some changes to params.py.

src/base/types.hh

@@ -89,6 +89,9 @@ class Cycles
     /** Explicit constructor assigning a value. */
     explicit Cycles(uint64_t _c) : c(_c) { }
 
+    /** Default constructor for parameter classes. */
+    Cycles() : c(0) { }
+
 #ifndef SWIG // keep the operators away from SWIG
 
     /** Converting back to the value type. */