ARM: dts: at91: sama5d2: mark secumod as a GPIO controller

ARM: dts: at91: sama5d2: mark secumod as a GPIO controller

The Security Module exposes the PIOBU pins which an be used
as regular GPIOs. The PIOBU pins are special because they do
not lose their voltage during suspend-to-mem.

This patch marks the secumod as a GPIO controller.

Signed-off-by: Andrei Stefanescu <andrei.stefanescu@microchip.com>
[razvan.stefanescu@microchip.com Updated title]
Signed-off-by: Razvan Stefanescu <razvan.stefanescu@microchip.com>
Link: https://lore.kernel.org/r/1573543139-8533-2-git-send-email-eugen.hristev@microchip.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>