RandomX: added parameter for scratchpad prefetch mode

`scratchpad_prefetch_mode` can have 4 values:
0: off
1: use `prefetcht0` instruction (default, same as previous XMRig versions)
2: use `prefetchnta` instruction (faster on Coffee Lake and a few other CPUs)
3: use `mov` instruction

src/crypto/rx/Rx.cpp

@@ -32,6 +32,7 @@
 #include "base/io/log/Log.h"
 #include "crypto/rx/RxConfig.h"
 #include "crypto/rx/RxQueue.h"
+#include "crypto/randomx/randomx.h"
 
 
 namespace xmrig {
@@ -99,6 +100,8 @@ bool xmrig::Rx::init(const T &seed, const RxConfig &config, const CpuConfig &cpu
         return true;
     }
 
+    randomx_set_scratchpad_prefetch_mode(config.scratchpadPrefetchMode());
+
     if (isReady(seed)) {
         return true;
     }