riscv: dts: spacemit: Add Milk-V Jupiter board device tree

Add initial support for the Milk-V Jupiter board [1], which is a Mini ITX
computer based on the SpacemiT K1/M1 Octa-Core X60 64-bit RISC-V SoC [2].

There are two variant for this board, one using the K1 chip and another
using the M1 chip. The main difference is that the M1 can run at a higher
frequency than the K1, thanks to its packaging.

For now, only a DTS for the K1 variant is added since there isn't support
yet for the X60 cores operating performance and thermal trip points.

The support is minimal, but at least allows to boot into a serial console.

Link: https://milkv.io/jupiter [1]
Link: https://www.spacemit.com/en/key-stone-k1 [2]
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Yixun Lan <dlan@gentoo.org>
Link: https://lore.kernel.org/r/20250214151700.666544-3-javierm@redhat.com
Signed-off-by: Yixun Lan <dlan@gentoo.org>

arch/riscv/boot/dts/spacemit/Makefile

@@ -1,2 +1,3 @@
 # SPDX-License-Identifier: GPL-2.0
 dtb-$(CONFIG_ARCH_SPACEMIT) += k1-bananapi-f3.dtb
+dtb-$(CONFIG_ARCH_SPACEMIT) += k1-milkv-jupiter.dtb

arch/riscv/boot/dts/spacemit/k1-milkv-jupiter.dts

@@ -0,0 +1,27 @@
+// SPDX-License-Identifier: GPL-2.0 OR MIT
+/*
+ * Copyright (C) 2024 Yangyu Chen <cyy@cyyself.name>
+ * Copyright (C) 2025 Javier Martinez Canillas <javierm@redhat.com>
+ */
+
+#include "k1.dtsi"
+#include "k1-pinctrl.dtsi"
+
+/ {
+	model = "Milk-V Jupiter (K1)";
+	compatible = "milkv,jupiter", "spacemit,k1";
+
+	aliases {
+		serial0 = &uart0;
+	};
+
+	chosen {
+		stdout-path = "serial0";
+	};
+};
+
+&uart0 {
+	pinctrl-names = "default";
+	pinctrl-0 = <&uart0_2_cfg>;
+	status = "okay";
+};