Add embassy-cortex-m crate.

- Move Interrupt and InterruptExecutor from `embassy` to `embassy-cortex-m`.
- Move Unborrow from `embassy` to `embassy-hal-common` (nothing in `embassy` requires it anymore)
- Move PeripheralMutex from `embassy-hal-common` to `embassy-cortex-m`.

embassy-stm32/src/dma/bdma.rs

@@ -3,7 +3,7 @@
 use core::sync::atomic::{fence, Ordering};
 use core::task::Waker;
 
-use embassy::interrupt::{Interrupt, InterruptExt};
+use crate::interrupt::{Interrupt, InterruptExt};
 use embassy::waitqueue::AtomicWaker;
 
 use crate::_generated::BDMA_CHANNEL_COUNT;

embassy-stm32/src/dma/dma.rs

@@ -1,7 +1,7 @@
 use core::sync::atomic::{fence, Ordering};
 use core::task::Waker;
 
-use embassy::interrupt::{Interrupt, InterruptExt};
+use crate::interrupt::{Interrupt, InterruptExt};
 use embassy::waitqueue::AtomicWaker;
 
 use crate::_generated::DMA_CHANNEL_COUNT;

embassy-stm32/src/dma/gpdma.rs

@@ -1,7 +1,7 @@
 use core::sync::atomic::{fence, Ordering};
 use core::task::Waker;
 
-use embassy::interrupt::{Interrupt, InterruptExt};
+use crate::interrupt::{Interrupt, InterruptExt};
 use embassy::waitqueue::AtomicWaker;
 
 use crate::_generated::GPDMA_CHANNEL_COUNT;

embassy-stm32/src/dma/mod.rs

@@ -10,13 +10,13 @@ mod gpdma;
 #[cfg(dmamux)]
 pub use dmamux::*;
 
+use crate::Unborrow;
 use core::future::Future;
 use core::marker::PhantomData;
 use core::mem;
 use core::pin::Pin;
 use core::task::Waker;
 use core::task::{Context, Poll};
-use embassy::util::Unborrow;
 use embassy_hal_common::unborrow;
 
 #[cfg(feature = "unstable-pac")]