[CPU] Implement mftb instruction natively.

When the cvars clock_no_scaling and clock_source_raw are set, tick counts will be directly calculated in the emitted code.

src/xenia/base/clock.cc

@@ -134,6 +134,11 @@ void Clock::set_guest_time_scalar(double scalar) {
   RecomputeGuestTickScalar();
 }
 
+std::pair<uint64_t, uint64_t> Clock::guest_tick_ratio() {
+  std::lock_guard<std::mutex> lock(tick_mutex_);
+  return guest_tick_ratio_;
+}
+
 uint64_t Clock::guest_tick_frequency() { return guest_tick_frequency_; }
 
 void Clock::set_guest_tick_frequency(uint64_t frequency) {

src/xenia/base/clock.h

@@ -43,6 +43,8 @@ class Clock {
   // Sets the guest time scalar, adjusting tick and wall clock speed.
   // Ex: 1x=normal, 2x=double speed, 1/2x=half speed.
   static void set_guest_time_scalar(double scalar);
+  // Get the tick ration between host and guest including time scaling if set.
+  static std::pair<uint64_t, uint64_t> guest_tick_ratio();
   // Guest ticks-per-second.
   static uint64_t guest_tick_frequency();
   // Sets the guest ticks-per-second.