Add blinky example for STM32F2

Default configuration is for NUCLEO-F207ZG board

examples/stm32f2/src/bin/blinky.rs

@@ -0,0 +1,29 @@
+#![no_std]
+#![no_main]
+#![feature(type_alias_impl_trait)]
+
+#[path = "../example_common.rs"]
+mod example_common;
+
+use embassy::executor::Spawner;
+use embassy::time::{Duration, Timer};
+use embassy_stm32::gpio::{Level, Output, Speed};
+use embassy_stm32::Peripherals;
+use example_common::*;
+
+#[embassy::main]
+async fn main(_spawner: Spawner, p: Peripherals) {
+    info!("Hello World!");
+
+    let mut led = Output::new(p.PB14, Level::High, Speed::Low);
+
+    loop {
+        info!("high");
+        led.set_high();
+        Timer::after(Duration::from_millis(1000)).await;
+
+        info!("low");
+        led.set_low();
+        Timer::after(Duration::from_millis(1000)).await;
+    }
+}