Fix PIO rx fifo status (#367)

* Implement embedded-hal 1.0.0-alpha.8 traits

* Add comment about missing SPI traits

* Fix doc of rx.is_empty() and add rx.is_full()

rp2040-hal/src/pio.rs

@@ -1138,10 +1138,15 @@ impl<SM: ValidStateMachine> Rx<SM> {
             .modify(|_, w| w.autopush().bit(enable))
     }
 
-    /// Indicate if the tx FIFO is full
+    /// Indicate if the rx FIFO is empty
     pub fn is_empty(&self) -> bool {
         self.register_block().fstat.read().rxempty().bits() & (1 << SM::id()) != 0
     }
+
+    /// Indicate if the rx FIFO is full
+    pub fn is_full(&self) -> bool {
+        self.register_block().fstat.read().rxfull().bits() & (1 << SM::id()) != 0
+    }
 }
 
 /// PIO TX FIFO handle.