rp/pio: remove PioPeripheral

merge into PioInstance instead. PioPeripheral was mostly a wrapper
around PioInstance anyway, and the way the wrapping was done required
PioInstanceBase<N> types where PIO{N} could've been used instead.

examples/rp/src/bin/ws2812-pio.rs

@@ -6,8 +6,8 @@ use defmt::*;
 use embassy_executor::Spawner;
 use embassy_rp::gpio::{self, Pin};
 use embassy_rp::pio::{
-    FifoJoin, PioCommon, PioCommonInstance, PioInstance, PioPeripheral, PioStateMachine, PioStateMachineInstance,
-    ShiftDirection, SmInstance,
+    FifoJoin, PioCommon, PioCommonInstance, PioInstance, PioStateMachine, PioStateMachineInstance, ShiftDirection,
+    SmInstance,
 };
 use embassy_rp::pio_instr_util;
 use embassy_rp::relocate::RelocatedProgram;