sam: simplify I2C peripheral declarations

This commit changes the I2C declarations so that the objects are
instantiated in each chip file (e.g. machine_atsamd21e18.go) and used to
define I2C0 (and similar) in the board file (e.g. board_qtpy.go). This
should make it easier to define new board files, and reduces the need
for separate *_baremetal.go files.

I have tested this the following way:

  - With the LIS3DH driver example on the Circuit Playground Express and
    the PyBadge.
  - With the LSM6DS3 driver example on the Arduino Nano 33 IoT.

They both still work fine.

1 files changed, 11 insertions, 0 deletions

diff --git a/src/machine/machine_atsamd51p20.go b/src/machine/machine_atsamd51p20.go
index 0d3776e82..733cc0c02 100644
--- a/src/machine/machine_atsamd51p20.go
+++ b/src/machine/machine_atsamd51p20.go
@@ -11,6 +11,17 @@ import "device/sam"
 
 const HSRAM_SIZE = 0x00040000
 
+var (
+	sercomI2CM0 = &I2C{Bus: sam.SERCOM0_I2CM, SERCOM: 0}
+	sercomI2CM1 = &I2C{Bus: sam.SERCOM1_I2CM, SERCOM: 1}
+	sercomI2CM2 = &I2C{Bus: sam.SERCOM2_I2CM, SERCOM: 2}
+	sercomI2CM3 = &I2C{Bus: sam.SERCOM3_I2CM, SERCOM: 3}
+	sercomI2CM4 = &I2C{Bus: sam.SERCOM4_I2CM, SERCOM: 4}
+	sercomI2CM5 = &I2C{Bus: sam.SERCOM5_I2CM, SERCOM: 5}
+	sercomI2CM6 = &I2C{Bus: sam.SERCOM6_I2CM, SERCOM: 6}
+	sercomI2CM7 = &I2C{Bus: sam.SERCOM7_I2CM, SERCOM: 7}
+)
+
 // This chip has five TCC peripherals, which have PWM as one feature.
 var (
 	TCC0 = (*TCC)(sam.TCC0)