Monero Cryptonight variants, and add one for v7

This is the first variant of many, with the intent to improve
Monero's resistance to ASICs and encourage mining decentralization.

src/device/device_ledger.cpp

@@ -511,7 +511,7 @@ namespace hw {
 
         char prekey[200];
         memmove(prekey, &this->buffer_recv[0], 200);
-        crypto::generate_chacha_key(&prekey[0], sizeof(prekey), key, true);
+        crypto::generate_chacha_key(&prekey[0], sizeof(prekey), key, 0, true);
 
         #ifdef DEBUG_HWDEVICE
         hw::ledger::check32("generate_chacha_key", "key", (char*)key_x.data(), (char*)key.data());