Core: Add VBI Frequency Override

This feature allows overriding the frequency of the Vertical Blank Interrupt. For many games, this means that their gameplay speed will change without affecting audio, which would be useful by itself (e.g. grinding in RPGs).

However, there are games that use delta time for their game logic, which allows them to be played at >60 FPS at the same gameplay speed!

Some games aren't dynamic though, and require a patch to adjust their game speed variable.

Source/Core/Core/NetPlayServer.cpp

@@ -1376,6 +1376,8 @@ bool NetPlayServer::SetupNetSettings()
   settings.allow_sd_writes = Config::Get(Config::MAIN_ALLOW_SD_WRITES);
   settings.oc_enable = Config::Get(Config::MAIN_OVERCLOCK_ENABLE);
   settings.oc_factor = Config::Get(Config::MAIN_OVERCLOCK);
+  settings.vi_oc_enable = Config::Get(Config::MAIN_VI_OVERCLOCK_ENABLE);
+  settings.vi_oc_factor = Config::Get(Config::MAIN_VI_OVERCLOCK);
 
   for (ExpansionInterface::Slot slot : ExpansionInterface::SLOTS)
   {
@@ -1603,6 +1605,8 @@ bool NetPlayServer::StartGame()
   spac << m_settings.allow_sd_writes;
   spac << m_settings.oc_enable;
   spac << m_settings.oc_factor;
+  spac << m_settings.vi_oc_enable;
+  spac << m_settings.vi_oc_factor;
 
   for (auto slot : ExpansionInterface::SLOTS)
     spac << static_cast<int>(m_settings.exi_device[slot]);