stm32/gpio: expose all functionality as inherent methods.

examples/stm32f4/src/bin/spi.rs

@@ -11,7 +11,6 @@ use embassy_stm32::gpio::{Level, Output, Speed};
 use embassy_stm32::spi::{Config, Spi};
 use embassy_stm32::time::Hertz;
 use embedded_hal::blocking::spi::Transfer;
-use embedded_hal::digital::v2::OutputPin;
 use example_common::*;
 
 #[entry]
@@ -35,9 +34,9 @@ fn main() -> ! {
 
     loop {
         let mut buf = [0x0Au8; 4];
-        unwrap!(cs.set_low());
+        cs.set_low();
         unwrap!(spi.transfer(&mut buf));
-        unwrap!(cs.set_high());
+        cs.set_high();
         info!("xfer {=[u8]:x}", buf);
     }
 }