m68k: dts: add i2c nodes

Add all the i2c nodes for each family, and add specific i2c
overwrites in the related board-specific dts.

Signed-off-by: Angelo Dureghello <angelo@kernel-space.org>
diff --git a/arch/m68k/dts/M5253DEMO.dts b/arch/m68k/dts/M5253DEMO.dts
index 515484a..a3f0706 100644
--- a/arch/m68k/dts/M5253DEMO.dts
+++ b/arch/m68k/dts/M5253DEMO.dts
@@ -20,3 +20,8 @@
 	status = "okay";
 };
 
+&i2c0 {
+	clock-frequency = <80000>;
+	u-boot,i2c-slave-addr = <0x7f>;
+	status = "okay";
+};