mvebu: enable PCA955x driver for clearfog to enable pcie and usb

Some of the PCIe and USB signals use a GPIO expander on I2C on ClearFog,
so enable the driver so that they can be configured to their required
values.

Signed-off-by: Jonas Gorski <jonas.gorski@gmail.com>
Acked-by: Felix Fietkau <nbd@nbd.name>