sam: move I2S0 to machine file

There is no need to put these in the board files as the I2S is the same
on all Microchip SAM D21 chips. This simplifies the code and avoids some
special *_baremetal.go files.

This change does not change the resulting binaries.

src/machine/board_arduino_mkrwifi1010.go

@@ -6,10 +6,6 @@
 //
 package machine
 
-import (
-	"device/sam"
-)
-
 // used to reset into bootloader
 const RESET_MAGIC_VALUE = 0x07738135
 
@@ -112,11 +108,6 @@ var (
 	NINA_SPI = SPI1
 )
 
-// I2S on the Arduino MKR WiFi 1010.
-var (
-	I2S0 = I2S{Bus: sam.I2S}
-)
-
 // USB CDC identifiers
 const (
 	usb_STRING_PRODUCT      = "Arduino MKR WiFi 1010"

src/machine/board_arduino_nano33_baremetal.go

@@ -1,12 +0,0 @@
-// +build sam,atsamd21,arduino_nano33
-
-package machine
-
-import (
-	"device/sam"
-)
-
-// I2S on the Arduino Nano 33.
-var (
-	I2S0 = I2S{Bus: sam.I2S}
-)

src/machine/board_circuitplay_express_baremetal.go

@@ -1,12 +0,0 @@
-// +build sam,atsamd21,circuitplay_express
-
-package machine
-
-import (
-	"device/sam"
-)
-
-// I2S on the Circuit Playground Express.
-var (
-	I2S0 = I2S{Bus: sam.I2S}
-)

src/machine/board_itsybitsy-m0.go

@@ -2,10 +2,6 @@
 
 package machine
 
-import (
-	"device/sam"
-)
-
 // used to reset into bootloader
 const RESET_MAGIC_VALUE = 0xf01669ef
 
@@ -97,11 +93,6 @@ const (
 	I2S_WS_PIN  = NoPin // TODO: figure out what this is on ItsyBitsy M0.
 )
 
-// I2S on the ItsyBitsy M0.
-var (
-	I2S0 = I2S{Bus: sam.I2S}
-)
-
 // USB CDC identifiers
 const (
 	usb_STRING_PRODUCT      = "Adafruit ItsyBitsy M0 Express"

src/machine/board_xiao.go

@@ -2,10 +2,6 @@
 
 package machine
 
-import (
-	"device/sam"
-)
-
 // used to reset into bootloader
 const RESET_MAGIC_VALUE = 0xf01669ef
 
@@ -90,11 +86,6 @@ const (
 	I2S_WS_PIN  = NoPin // TODO: figure out what this is on Xiao
 )
 
-// I2S on the Xiao
-var (
-	I2S0 = I2S{Bus: sam.I2S}
-)
-
 // USB CDC identifiers
 const (
 	usb_STRING_PRODUCT      = "Seeed XIAO M0"

src/machine/machine_atsamd21.go

@@ -897,6 +897,8 @@ type I2S struct {
 	Bus *sam.I2S_Type
 }
 
+var I2S0 = I2S{Bus: sam.I2S}
+
 // Configure is used to configure the I2S interface. You must call this
 // before you can use the I2S bus.
 func (i2s I2S) Configure(config I2SConfig) {