Add Kernel::impl::get_tick_count() stub

Author: kjbracey

UNITTESTS/stubs/Kernel_stub.cpp

@@ -20,6 +20,11 @@
 namespace rtos {
 
 uint64_t Kernel::get_ms_count()
+{
+    return impl::get_tick_count();
+
+}
+uint64_t Kernel::impl::get_tick_count()
 {
     return 20;
 }