ARM: at91/dt: add SRAM nodes

Add nodes for the SRAM available on atmel SoCs
For the at91sam9260 and the at91sam9g20, address mirroring is used to create a
single contiguous SRAM range instead of declaring two separate banks.

Also remove leftover TODOs in the sam9g45 file

Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Acked-by: Boris Brezillon <boris.brezillon@free-electrons.com>
[nicolas.ferre@atmel.com: correct at91sam9rl sram size => 0x10000]
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>

arch/arm/boot/dts/at91sam9n12.dtsi

@@ -64,6 +64,11 @@
 		};
 	};
 
+	sram: sram@00300000 {
+		compatible = "mmio-sram";
+		reg = <0x00300000 0x8000>;
+	};
+
 	ahb {
 		compatible = "simple-bus";
 		#address-cells = <1>;