[core, frontend] Add Custom CPU Ticks option (#217)

Co-authored-by: Gamer64 <76565986+Gamer64ytb@users.noreply.github.com>
Co-authored-by: crueter <swurl@swurl.xyz>
Reviewed-on: #217

src/core/core_timing.cpp

@@ -172,7 +172,9 @@ void CoreTiming::UnscheduleEvent(const std::shared_ptr<EventType>& event_type,
 }
 
 void CoreTiming::AddTicks(u64 ticks_to_add) {
-    cpu_ticks += ticks_to_add;
+    cpu_ticks = Settings::values.use_custom_cpu_ticks.GetValue() 
+            ? Settings::values.cpu_ticks.GetValue() 
+            : cpu_ticks + ticks_to_add;
     downcount -= static_cast<s64>(cpu_ticks);
 }