nrf5340: add internal capacitor config

[0e4ef622]

config for the optional internal capacitors for the HFXO/LFXO on the nrf5340

[alexbohm]

Thanks! You just beat me by hours to asking about this since a BC40C module I was trying didn't have external capacitors.

I tested this with a custom board using that module and this code modified from the blinky.rs example. Seems to be happily blinking away!

#![no_std]
#![no_main]

use embassy_executor::Spawner;
use embassy_nrf::config::{HfclkSource, HfxoCapacitance, InternalCapacitors, LfclkSource, LfxoCapacitance};
use embassy_nrf::gpio::{Level, Output, OutputDrive};
use embassy_time::Timer;
use {defmt_rtt as _, panic_probe as _};

#[embassy_executor::main]
async fn main(_spawner: Spawner) {
    let mut config: embassy_nrf::config::Config = Default::default();

    config.hfclk_source = HfclkSource::ExternalXtal;
    config.lfclk_source = LfclkSource::ExternalXtal;

    config.internal_capacitors = InternalCapacitors {
        hfxo: Some(HfxoCapacitance::_15_5pF),
        lfxo: Some(LfxoCapacitance::_7pF),
    };

    let p = embassy_nrf::init(config);
    let mut led = Output::new(p.P1_11, Level::Low, OutputDrive::Standard);

    loop {
        led.set_high();
        Timer::after_millis(300).await;
        led.set_low();
        Timer::after_millis(300).await;
    }
}