gpio: direct hardware access for pin peripheral

using most recent RTOS for reference, allows us to skip Arduino
layer when configuring things. especially useful for UART
re-implementation that does not involve magic pin function modes

adjust our terminal command to really show valid pins and their modes

code/espurna/button.cpp

@@ -21,7 +21,6 @@ Copyright (C) 2019-2021 by Maxim Prokhorov <prokhorov dot max at outlook dot com
 #include "system.h"
 #include "ws.h"
 
-#include "gpio_pin.h"
 #include "mcp23s08_pin.h"
 
 #include <bitset>