arm: kirkwood: add DT spi0 alias to LaCie boards

The spi0 alias is needed by the environment code to retrieve the SPI
flash. This patch adds some -u-boot.dtsi files, providing the spi0
aliases, for all the following Kirkwood-based LaCie boards:

- d2 Network v2
- Internet Space v2
- 2Big Network v2
- Network Space v2
- Network Space Lite v2
- Network Space Max v2
- Network Space Mini v2

Note that this -u-boot.dtsi files will be removed as soon as the spi0
aliases will be available in the upstream Linux dtsi files.

Signed-off-by: Simon Guinot <simon.guinot@sequanux.org>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Stefan Roese <sr@denx.de>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>
diff --git a/arch/arm/dts/kirkwood-ns2-u-boot.dtsi b/arch/arm/dts/kirkwood-ns2-u-boot.dtsi
new file mode 100644
index 0000000..1f3b185
--- /dev/null
+++ b/arch/arm/dts/kirkwood-ns2-u-boot.dtsi
@@ -0,0 +1,7 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/ {
+	aliases {
+		spi0 = &spi0;
+	};
+};