py/scheduler: Move mp_keyboard_interrupt from lib/utils to py core.

This function is tightly coupled to the state and behaviour of the
scheduler, and is a core part of the runtime: to schedule a pending
exception.  So move it there.

py/runtime.h

@@ -64,6 +64,7 @@ extern const byte mp_binary_op_method_name[];
 void mp_init(void);
 void mp_deinit(void);
 
+void mp_keyboard_interrupt(void);
 void mp_handle_pending(bool raise_exc);
 void mp_handle_pending_tail(mp_uint_t atomic_state);