ARM: at91: Documentation: update the sama5d2 entry

Update the Atmel SoC entry for SAMA5D2 with all the product variants. Add the
datasheet web link, now that it's available, for instant access to full product
documentation.

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>

Documentation/arm/Atmel/README

@@ -91,9 +91,15 @@ the Atmel website: http://www.atmel.com.
           http://www.atmel.com/Images/Atmel-11238-32-bit-Cortex-A5-Microcontroller-SAMA5D4_Datasheet.pdf
 
       - sama5d2 family
-        - sama5d27
+        - sama5d21
+        - sama5d22
+        - sama5d23
+        - sama5d24
+        - sama5d26
+        - sama5d27 (device superset)
+        - sama5d28 (device superset + environmental monitors)
         + Datasheet
-          Coming soon
+          http://www.atmel.com/Images/Atmel-11267-32-bit-Cortex-A5-Microcontroller-SAMA5D2_Datasheet.pdf
 
 
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