Standardize SAMD51 UART settings (#1155)

* machine/samd51: standardize samd51 uart settings

src/machine/board_itsybitsy-m4.go

@@ -1,9 +1,7 @@
-// +build sam,atsamd51,itsybitsy_m4
+// +build itsybitsy_m4
 
 package machine
 
-import "device/sam"
-
 // used to reset into bootloader
 const RESET_MAGIC_VALUE = 0xf01669ef
 
@@ -51,30 +49,17 @@ const (
 	UART_RX_PIN = D0
 )
 
-// UART1 var is on SERCOM3, defined in atsamd51.go
-
-// UART2 pins
 const (
 	UART2_TX_PIN = A4
 	UART2_RX_PIN = D2
 )
 
-// UART2 var is on SERCOM0, defined in atsamd51.go
-
 // I2C pins
 const (
 	SDA_PIN = PA12 // SDA: SERCOM2/PAD[0]
 	SCL_PIN = PA13 // SCL: SERCOM2/PAD[1]
 )
 
-// I2C on the ItsyBitsy M4.
-var (
-	I2C0 = I2C{
-		Bus:    sam.SERCOM2_I2CM,
-		SERCOM: 2,
-	}
-)
-
 // SPI pins
 const (
 	SPI0_SCK_PIN  = PA01 // SCK: SERCOM1/PAD[1]
@@ -82,14 +67,6 @@ const (
 	SPI0_MISO_PIN = PB23 // MISO: SERCOM1/PAD[3]
 )
 
-// SPI on the ItsyBitsy M4.
-var (
-	SPI0 = SPI{
-		Bus:    sam.SERCOM1_SPIM,
-		SERCOM: 1,
-	}
-)
-
 // USB CDC identifiers
 const (
 	usb_STRING_PRODUCT      = "Adafruit ItsyBitsy M4"