dt-bindings: i2c: atmel,at91sam: drop unneeded address/size-cells

The reference i2c-controller.yaml already defines 'address-cells' and
'size-cells', so drop them from list of properties.  Drop them as well
from required properties, even though i2c-controller.yaml does not
require them, because I2C controller could be enabled without any
children in DTS for user-space usage.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>