Gpio interface improvements

Common gpio functions for lpc21 and stm32 architectures like:
- gpio_setup(GPIOA, GPIO1)
- gpio_clear(GPIOA, GPIO1)
- gpio_setup_output(GPIOA, GPIO1)
- gpio_setup_input(GPIOA, GPIO1)

you can also set multiple gpios at once, e.g.: `gpio_set(GPIOA, GPIO1 | GPIO2)`

Please test....