Add MBX support, mailbox for communication across multicore or RTOS tasks

[andelf]

• message word(u32) API: send/recv interface
• message queue(FIFO) API: send_fifo/recv_fifo/Stream interface
• Demo code
• Design consideration: eliminate peripheral generic parameter? - DONE

Demo usage:

bind_interrupts!(struct Irqs {
    MBX0A => hal::mbx::InterruptHandler<peripherals::MBX0A>;
    MBX0B => hal::mbx::InterruptHandler<peripherals::MBX0B>;
});


#[embassy_executor::task]
async fn mailbox(mbox: Mbx<'static>) {
    let mut mbox = mbox;
    let mut i = 345;
    loop {
        defmt::info!("[task0] sending {}", i);
        mbox.send_fifo(i).await; // will block until fifo has space
        i += 1;

        Timer::after_millis(100).await; // faster
    }
}

let mut outbox = Mbx::new(p.MBX0B, Irqs);
while let Some(val) = outbox.next().await {
            defmt::info!("[main] Received: {}", val);
            Timer::after_millis(1000).await; // slower
}