renesas-ra: Replace MICROPY_EVENT_POLL_HOOK with mp_event_wait.

Basic update to the renesas-ra port to replace the traditional
`MICROPY_EVENT_POLL_HOOK` with the newer mp_event_wait API as appropriate.

Signed-off-by: Andrew Leech <andrew@alelec.net>

ports/renesas-ra/mphalport.c

@@ -104,7 +104,7 @@ int mp_hal_stdin_rx_chr(void) {
             return dupterm_c;
         }
         #endif
-        MICROPY_EVENT_POLL_HOOK
+        mp_event_wait_indefinite();
     }
 }