dt-bindings: rng: atmel-trng: add new compatible

Add compatible for new IP found on sam9x60 SoC.
Signed-off-by: Codrin Ciubotariu <codrin.ciubotariu@microchip.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Documentation/devicetree/bindings/rng/atmel-trng.txt

 Atmel TRNG (True Random Number Generator) block
 
 Required properties:
-- compatible : Should be "atmel,at91sam9g45-trng"
+- compatible : Should be "atmel,at91sam9g45-trng" or "microchip,sam9x60-trng"
 - reg : Offset and length of the register set of this block
 - interrupts : the interrupt number for the TRNG block
 - clocks: should contain the TRNG clk source