Add per-core EXTI support

* Generate a core index put into the PAC for the peripherals to use as
  index into registers.
* Add EXTI v2 which uses CORE_INDEX to index exti registers

examples/stm32wl55/src/bin/button_exti.rs

@@ -0,0 +1,34 @@
+#![no_std]
+#![no_main]
+#![feature(trait_alias)]
+#![feature(type_alias_impl_trait)]
+#![allow(incomplete_features)]
+
+#[path = "../example_common.rs"]
+mod example_common;
+use embassy::executor::Spawner;
+use embassy_stm32::dbgmcu::Dbgmcu;
+use embassy_stm32::exti::ExtiInput;
+use embassy_stm32::gpio::{Input, Pull};
+use embassy_stm32::Peripherals;
+use embassy_traits::gpio::{WaitForFallingEdge, WaitForRisingEdge};
+use example_common::*;
+
+#[embassy::main]
+async fn main(_spawner: Spawner, p: Peripherals) {
+    info!("Hello World!");
+
+    unsafe { Dbgmcu::enable_all() };
+
+    let button = Input::new(p.PA0, Pull::Up);
+    let mut button = ExtiInput::new(button, p.EXTI0);
+
+    info!("Press the USER button...");
+
+    loop {
+        button.wait_for_falling_edge().await;
+        info!("Pressed!");
+        button.wait_for_rising_edge().await;
+        info!("Released!");
+    }
+}