rp: generalize adc inputs from pins to channels

this lets us treat pins and the temperature sensor uniformly using the
same interface. uniformity in turn lets us add more adc features without
combinatorial explosion of methods and types needed to handle them all.

embassy-rp/src/lib.rs

@@ -183,6 +183,7 @@ embassy_hal_internal::peripherals! {
     FLASH,
 
     ADC,
+    ADC_TEMP_SENSOR,
 
     CORE1,