dt-bindings: i2c: at91: add new compatible

Add compatible for new Microchip SoC, sam9x60

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>
Acked-by: Ludovic Desroches <ludovic.desroches@microchip.com>
Reviewed-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>