rp2040: move UART0 and UART1 to common file

This is makes it easier to use these in simulation, plus it avoids
duplication. The only downside I see is that more UARTs get defined than
a board supports, but no existing code should break (no UARTs get
renamed for example).

src/machine/board_nano-rp2040.go

@@ -11,11 +11,6 @@
 // - Nano RP2040 Connect technical reference: https://docs.arduino.cc/tutorials/nano-rp2040-connect/rp2040-01-technical-reference
 package machine
 
-import (
-	"device/rp"
-	"runtime/interrupt"
-)
-
 // Digital Pins
 const (
 	D2  Pin = GPIO25
@@ -125,27 +120,7 @@ const (
 	UART_RX_PIN  = UART0_RX_PIN
 )
 
-// UART on the RP2040
-var (
-	UART0  = &_UART0
-	_UART0 = UART{
-		Buffer: NewRingBuffer(),
-		Bus:    rp.UART0,
-	}
-
-	UART1  = &_UART1
-	_UART1 = UART{
-		Buffer: NewRingBuffer(),
-		Bus:    rp.UART1,
-	}
-
-	// UART_NINA on the Arduino Nano RP2040 connects to the NINA HCI.
-	UART_NINA = UART1
-)
+// UART_NINA on the Arduino Nano RP2040 connects to the NINA HCI.
+var UART_NINA = UART1
 
 var DefaultUART = UART0
-
-func init() {
-	UART0.Interrupt = interrupt.New(rp.IRQ_UART0_IRQ, _UART0.handleInterrupt)
-	UART1.Interrupt = interrupt.New(rp.IRQ_UART1_IRQ, _UART1.handleInterrupt)
-}