ARM: dts: at91: fix sram nodes

The ranges, #address-cells and #size-cells properties are mandatory, add
them to the sram nodes.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Reviewed-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Link: https://lore.kernel.org/r/20200831171129.3886857-4-alexandre.belloni@bootlin.com