stm32/gpio: expose all functionality as inherent methods.

examples/stm32l4/src/bin/button.rs

@@ -5,7 +5,6 @@
 #[path = "../example_common.rs"]
 mod example_common;
 use embassy_stm32::gpio::{Input, Pull};
-use embedded_hal::digital::v2::InputPin;
 use example_common::*;
 
 #[cortex_m_rt::entry]
@@ -17,7 +16,7 @@ fn main() -> ! {
     let button = Input::new(p.PC13, Pull::Up);
 
     loop {
-        if unwrap!(button.is_high()) {
+        if button.is_high() {
             info!("high");
         } else {
             info!("low");