Make interrupt module more standard.

- Move typelevel interrupts to a special-purpose mod: `embassy_xx::interrupt::typelevel`.
- Reexport the PAC interrupt enum in `embassy_xx::interrupt`.

This has a few advantages:
- The `embassy_xx::interrupt` module is now more "standard".
  - It works with `cortex-m` functions for manipulating interrupts, for example.
  - It works with RTIC.
- the interrupt enum allows holding value that can be "any interrupt at runtime", this can't be done with typelevel irqs.
- When "const-generics on enums" is stable, we can remove the typelevel interrupts without disruptive changes to `embassy_xx::interrupt`.

embassy-rp/src/dma.rs

@@ -4,11 +4,11 @@ use core::pin::Pin;
 use core::sync::atomic::{compiler_fence, Ordering};
 use core::task::{Context, Poll};
 
-use embassy_cortex_m::interrupt::Interrupt;
 use embassy_hal_common::{impl_peripheral, into_ref, Peripheral, PeripheralRef};
 use embassy_sync::waitqueue::AtomicWaker;
 use pac::dma::vals::DataSize;
 
+use crate::interrupt::InterruptExt;
 use crate::pac::dma::vals;
 use crate::{interrupt, pac, peripherals};
 
@@ -29,12 +29,12 @@ unsafe fn DMA_IRQ_0() {
 }
 
 pub(crate) unsafe fn init() {
-    interrupt::DMA_IRQ_0::disable();
-    interrupt::DMA_IRQ_0::set_priority(interrupt::Priority::P3);
+    interrupt::DMA_IRQ_0.disable();
+    interrupt::DMA_IRQ_0.set_priority(interrupt::Priority::P3);
 
     pac::DMA.inte0().write(|w| w.set_inte0(0xFFFF));
 
-    interrupt::DMA_IRQ_0::enable();
+    interrupt::DMA_IRQ_0.enable();
 }
 
 pub unsafe fn read<'a, C: Channel, W: Word>(