serial: add a serial driver for the SAM0 family.

Signed-off-by: Michael Hope <mlhx@google.com>

dts/bindings/serial/atmel,sam0-uart.yaml

@@ -0,0 +1,30 @@
+---
+title: Atmel SAM0 SERCOM UART driver
+id: atmel,sam0-uart
+version: 0.1
+
+description: >
+    This binding gives a base representation of the Atmel SAM0 SERCOM UART driver
+
+inherits:
+    !include uart.yaml
+
+properties:
+    compatible:
+      type: string
+      category: required
+      description: compatible strings
+      constraint: "atmel,sam0-uart"
+
+    reg:
+      type: array
+      description: mmio register space
+      generation: define
+      category: required
+
+    interrupts:
+      type: array
+      category: required
+      description: required interrupts
+      generation: define
+...