PID loop development + move rate control to own source files

examples/xua_lite_example/src/rate_controller.h

@@ -0,0 +1,17 @@
+#include <stdint.h>
+#include <limits.h>
+
+typedef int32_t xua_lite_fixed_point_t;
+
+typedef struct pid_state_t{
+  xua_lite_fixed_point_t fifo_level_filtered_old;
+  xua_lite_fixed_point_t fifo_level_accum;
+} pid_state_t;
+
+
+//USB Adaptive mode helper
+void do_rate_control(int fill_level, pid_state_t *pid_state, int *clock_nudge);
+
+//USB Asynch mode helper
+void do_feedback_calculation(unsigned &sof_count, const unsigned mclk_hz, unsigned mclk_port_counter,unsigned &mclk_port_counter_old
+                                ,long long &feedback_value, unsigned &mod_from_last_time, unsigned fb_clocks[1]);