ARM: dts: at91: sama5d2_ptc_ek: Add comments to describe the aliases

Indicate which i2c alias is for which connector on the board.
Specify that serial0 is for DBGU. This eases tester's life.
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Link: https://lore.kernel.org/r/20200514050301.147442-17-tudor.ambarus@microchip.comSigned-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

arch/arm/boot/dts/at91-sama5d2_ptc_ek.dts

@@ -18,9 +18,9 @@ / {
 	compatible = "atmel,sama5d2-ptc_ek", "atmel,sama5d2", "atmel,sama5";
 
 	aliases {
-		serial0 = &uart0;
-		i2c0	= &i2c0;
-		i2c1	= &i2c1;
+		serial0 = &uart0;	/* DBGU */
+		i2c0	= &i2c0;	/* mikroBUS 1 */
+		i2c1	= &i2c1;	/* XPRO EXT1 */
 		i2c2	= &i2c2;
 	};