PowerPC: Add functions to read/write the full timebase value

Allows us to get rid of a silly pointer cast and deduplicate some code
from the front-end when it comes to reading the value.

Source/Core/Core/PowerPC/PowerPC.cpp

@@ -349,6 +349,18 @@ void RunLoop()
   Host_UpdateDisasmDialog();
 }
 
+u64 ReadFullTimeBaseValue()
+{
+  u64 value;
+  std::memcpy(&value, &TL, sizeof(value));
+  return value;
+}
+
+void WriteFullTimeBaseValue(u64 value)
+{
+  std::memcpy(&TL, &value, sizeof(value));
+}
+
 void UpdatePerformanceMonitor(u32 cycles, u32 num_load_stores, u32 num_fp_inst)
 {
   switch (MMCR0.PMC1SELECT)