LV2: Improve sys_timer_usleep by using CPU usermode waiting

* Linux: set timerslack to minimum value
- Linux delays the wakeup of threads to save power, this feature isn't needed for this application

* Utils: Add detection for waitpkg and monitorx extensions
- These instructions are used for user mode wait instructions

* lv2: Use user mode wait instructions instead of yielding when appropriate

rpcs3/main.cpp

@@ -1049,6 +1049,11 @@ int main(int argc, char** argv)
 		}
 	}
 
+// Set timerslack value for Linux. The default value is 50,000ns. Change this to just 1 since we value precise timers.
+#ifdef __linux__
+	prctl(PR_SET_TIMERSLACK, 1, 0, 0, 0);
+#endif
+
 #ifdef _WIN32
 	// Create dummy permanent low resolution timer to workaround messing with system timer resolution
 	QTimer* dummy_timer = new QTimer(app.data());