Enable PCNT on ESP32-S31, rework API

[bugadani]

PCNT now follows the one channel - one singleton pattern. There is no common setup, just a bit of mutexing because of some shared register.

Changelog

esp-hal

• Added: PCNT support for ESP32-S31
• Changed: PCNT units are constructed from PCNTn_UNITm singletons instead of a Pcnt driver.

Migration guide

esp-hal/PCNT driver

Construct units from singletons

Pcnt::new and the unit0…unitN fields are gone. Build a Unit from a PCNTn_UNITm singleton (PCNT is block 0). Unit no longer has a unit-index type parameter.

-let pcnt = Pcnt::new(peripherals.PCNT);
-let mut unit0 = pcnt.unit0;
+let mut unit0 = Unit::new(peripherals.PCNT0_UNIT0);

On ESP32-S31, PCNT1_UNIT0...PCNT1_UNIT3 is also available.

Register interrupt handlers on the unit (unit0.set_interrupt_handler(...)). The hardware still has one IRQ per register block; the driver dispatches to the unit whose status bit is set.

[bugadani]

/hil full

[github-actions]

Triggered full HIL run for #6191.

Run: https://github.com/esp-rs/esp-hal/actions/runs/32751192791

Status update: HIL (full) run is still in progress or status unknown.