Benchmark support for GhostRider (offline only)

Command line:
```
./xmrig --bench=250K -a gr --rotation 15
```
Where `rotation` is an integer between 0 and 19 (inclusive).

src/base/kernel/interfaces/IConfig.h

@@ -87,6 +87,7 @@ public:
         SpendSecretKey       = 1055,
         DaemonZMQPortKey     = 1056,
         HugePagesJitKey      = 1057,
+        RotationKey          = 1058,
 
         // xmrig common
         CPUPriorityKey       = 1021,