boards: enclustra: mercury_xu: move unmodified sram0 from SoC to board DT

Move the unmodified sram0 memory area declaration to this board's
device tree due to its removal from the SoC device tree.

Signed-off-by: Immo Birnbaum <[email protected]>

Author: ibirnbaum

boards/enclustra/mercury_xu/mercury_xu.dts

@@ -12,6 +12,11 @@
 	model = "Mercury XU";
 	compatible = "enclustra,mercury_xu";
 
+	sram0: memory@0 {
+		compatible = "mmio-sram";
+		reg = <0 DT_SIZE_M(64)>;
+	};
+
 	chosen {
 		zephyr,console = &uart0;
 		zephyr,shell-uart = &uart0;