Build nOS-V with PAPI support

To support the new instrumentation for HWC it would be useful to already
build nOS-V with PAPI support enabled. The enablePapi switch allows it
to be disabled with `nosv.override { enablePapi = false; }`.

pkgs/nosv/default.nix

@@ -7,6 +7,7 @@
 , numactl
 , hwloc
 , papi
+, enablePapi ? true
 , cacheline ? 64 # bits
 , ovni ? null
 , useGit ? false
@@ -57,6 +58,5 @@ in
       numactl
       hwloc
       ovni
-      papi
-    ];
+    ] ++ lib.optionals enablePapi [ papi ];
   }