Standardize SAMD51 UART settings (#1155)

* machine/samd51: standardize samd51 uart settings

src/machine/board_pyportal_baremetal.go

@@ -0,0 +1,37 @@
+// +build sam,atsamd51,pyportal
+
+package machine
+
+import (
+	"device/sam"
+	"runtime/interrupt"
+)
+
+var (
+	UART1 = UART{
+		Buffer: NewRingBuffer(),
+		Bus:    sam.SERCOM4_USART_INT,
+		SERCOM: 4,
+	}
+)
+
+func init() {
+	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM4_2, UART1.handleInterrupt)
+}
+
+// I2C on the PyPortal.
+var (
+	I2C0 = I2C{
+		Bus:    sam.SERCOM5_I2CM,
+		SERCOM: 5,
+	}
+)
+
+// SPI on the PyPortal.
+var (
+	SPI0 = SPI{
+		Bus:    sam.SERCOM2_SPIM,
+		SERCOM: 2,
+	}
+	NINA_SPI = SPI0
+)