ARM: at91: Documentation: add sam9x60 product and datasheet

Add the new SAM9X60 ARM926-based SoC from Microchip and its associated
datasheet.
Signed-off-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Link: https://lore.kernel.org/r/20200110090103.7728-1-nicolas.ferre@microchip.comSigned-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

Documentation/arm/microchip.rst

@@ -92,6 +92,12 @@ the Microchip website: http://www.microchip.com.
 
           http://ww1.microchip.com/downloads/en/DeviceDoc/DS60001517A.pdf
 
+      - sam9x60
+
+          * Datasheet
+
+          http://ww1.microchip.com/downloads/en/DeviceDoc/SAM9X60-Data-Sheet-DS60001579A.pdf
+
     * ARM Cortex-A5 based SoCs
       - sama5d3 family