ARM: dts: at91: sama5d2: map securam as device

Due to strobe signal not being propagated from CPU to securam
the securam needs to be mapped as device or strongly ordered memory
to work properly. Otherwise, updating to one offset may affect
the adjacent locations in securam.

Fixes: d4ce5f44 ("ARM: dts: at91: sama5d2: Add securam node")
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Link: https://lore.kernel.org/r/1606903025-14197-3-git-send-email-claudiu.beznea@microchip.com