ARM: at91: Call at91_register_devices in the board files

Make every board call the register_devices callback so that the devices
declared by the SoC are registered.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>