Add implementation of async trait for STM32 I2C v2

* Add DMA read implementation for I2C v2
* Add example using DMA for I2C

examples/stm32l4/src/bin/i2c_dma.rs

@@ -0,0 +1,35 @@
+#![no_std]
+#![no_main]
+#![feature(type_alias_impl_trait)]
+
+#[path = "../example_common.rs"]
+mod example_common;
+
+use embassy::executor::Spawner;
+use embassy::traits::i2c::I2c as I2cTrait;
+use embassy_stm32::i2c::I2c;
+use embassy_stm32::interrupt;
+use embassy_stm32::time::Hertz;
+use embassy_stm32::Peripherals;
+use example_common::{info, unwrap};
+
+const ADDRESS: u8 = 0x5F;
+const WHOAMI: u8 = 0x0F;
+
+#[embassy::main]
+async fn main(_spawner: Spawner, p: Peripherals) -> ! {
+    let irq = interrupt::take!(I2C2_EV);
+    let mut i2c = I2c::new(
+        p.I2C2,
+        p.PB10,
+        p.PB11,
+        irq,
+        p.DMA1_CH4,
+        p.DMA1_CH5,
+        Hertz(100_000),
+    );
+
+    let mut data = [0u8; 1];
+    unwrap!(i2c.write_read(ADDRESS, &[WHOAMI], &mut data).await);
+    info!("Whoami: {}", data[0]);
+}