rp/pio: enable pio interrupts only once

since we never actually *disable* these interrupts for any length of
time we can simply enable them globally. we also initialize all pio
interrupt flags to not cause system interrupts since state machine
irqa are not necessarily meant to cause a system interrupt when set. the
fifo interrupts are sticky and can likewise only be cleared inside the
handler by disabling them.

embassy-rp/src/lib.rs

@@ -156,6 +156,7 @@ pub fn init(_config: config::Config) -> Peripherals {
         #[cfg(feature = "time-driver")]
         timer::init();
         dma::init();
+        pio::init();
     }
 
     peripherals