arm: dts: add U-Boot overrides for Genio 520 and 720 SD card

Add U-Boot-specific device tree overrides for the Genio 520 and 720 EVK
boards. These are needed to enable SD card support in U-Boot due to
current driver limitations. It is expected that these files will remain
after eventually converting these to CONFIG_OF_UPSTREAM, so we use
separate .u-boot.dtsi files for this.

Reviewed-by: Julien Stephan <jstephan@baylibre.com>
Link: https://patch.msgid.link/20260316-mtk-ext-mmc-boot-v1-2-1aae51a44705@baylibre.com
Signed-off-by: David Lechner <dlechner@baylibre.com>

arch/arm/dts/mt8371-genio-520-evk-u-boot.dtsi

@@ -0,0 +1,3 @@
+// SPDX-License-Identifier: (GPL-2.0-only OR MIT)
+
+#include "mt8371-genio-common-u-boot.dtsi"

arch/arm/dts/mt8371-genio-common-u-boot.dtsi

@@ -0,0 +1,28 @@
+// SPDX-License-Identifier: (GPL-2.0-only OR MIT)
+/*
+ * Copyright (C) 2026 MediaTek Inc.
+ */
+
+&mmc1 {
+	/* U-Boot driver doesn't support UHS yet. */
+	/delete-property/ sd-uhs-sdr50;
+	/delete-property/ sd-uhs-sdr104;
+	mmc-no-1-8-v;
+};
+
+/*
+ * Needed to trigger U-Boot auto-set-voltage. Default voltages for these
+ * supplies at boot are incorrect and U-Boot MMC drivers don't set them.
+ */
+
+&mt6359_vpa_buck_reg {
+	regulator-min-microvolt = <3000000>;
+	regulator-max-microvolt = <3000000>;
+	regulator-always-on;
+};
+
+&mt6359_vsim1_ldo_reg {
+	regulator-min-microvolt = <3000000>;
+	regulator-max-microvolt = <3000000>;
+	regulator-always-on;
+};

arch/arm/dts/mt8391-genio-720-evk-u-boot.dtsi

@@ -0,0 +1,3 @@
+// SPDX-License-Identifier: (GPL-2.0-only OR MIT)
+
+#include "mt8371-genio-common-u-boot.dtsi"

board/mediatek/MAINTAINERS

@@ -1,6 +1,9 @@
 MT8189/MT8371/MT8391 EVK
 M:	Macpaul Lin <macpaul.lin@mediatek.com>
 S:	Maintained
+F:	arch/arm/dts/mt8371-genio-520-evk-u-boot.dtsi
+F:	arch/arm/dts/mt8371-genio-common-u-boot.dtsi
+F:	arch/arm/dts/mt8391-genio-720-evk-u-boot.dtsi
 F:	configs/mt8189.config
 F:	configs/mt8371_genio_520_evk_defconfig
 F:	configs/mt8391_genio_720_evk_defconfig