boards/youyeetoo-yy3588: switch to mainline U-Boot v2026.04

The radxa vendor U-Boot no longer boots the board, so move every
kernel branch to mainline v2026.04 with binman u-boot-rockchip.bin
and rkbin BL31 plus DDR blobs, mirroring youyeetoo-r1-v3. Boot order
prefers SD, then NVMe, then eMMC.

Signed-off-by: SuperKali <hello@superkali.me>

Author: SuperKali

config/boards/youyeetoo-yy3588.conf

@@ -15,6 +15,35 @@ BOOT_FDT_FILE="rockchip/rk3588-youyeetoo-yy3588.dtb"
 BOOT_SCENARIO="spl-blobs"
 ASOUND_STATE="asound.state.youyeetoo-yy3588"
 
+function post_family_config__youyeetoo_yy3588_use_mainline_uboot() {
+	display_alert "$BOARD" "Using mainline U-Boot for $BOARD / $BRANCH" "info"
+
+	declare -g BOOTCONFIG="youyeetoo-yy3588-rk3588_defconfig"
+	declare -g BOOTDELAY=1
+	declare -g BOOTSOURCE="https://github.com/u-boot/u-boot.git"
+	declare -g BOOTBRANCH="tag:v2026.04"
+	declare -g BOOTPATCHDIR="v2026.04"
+	unset BOOT_FDT_FILE
+
+	# Don't set BOOTDIR, allow shared U-Boot source directory for disk space efficiency
+	declare -g UBOOT_TARGET_MAP="BL31=${RKBIN_DIR}/${BL31_BLOB} ROCKCHIP_TPL=${RKBIN_DIR}/${DDR_BLOB};;u-boot-rockchip.bin"
+
+	# Disable stuff from rockchip64_common; we're using binman here which does all the work already
+	unset uboot_custom_postprocess write_uboot_platform write_uboot_platform_mtd
+
+	# Just use the binman-provided u-boot-rockchip.bin, which is ready-to-go
+	function write_uboot_platform() {
+		dd "if=$1/u-boot-rockchip.bin" "of=$2" bs=32k seek=1 conv=notrunc status=none
+	}
+}
+
+function pre_config_uboot_target__youyeetoo_yy3588_patch_rockchip_common_boot_order() {
+	declare -a rockchip_uboot_targets=("mmc1" "nvme" "mmc0" "scsi" "usb" "pxe" "dhcp") # mmc1=SD, mmc0=eMMC
+	display_alert "u-boot for ${BOARD}/${BRANCH}" "u-boot: adjust boot order to '${rockchip_uboot_targets[*]}'" "info"
+	sed -i -e "s/#define BOOT_TARGETS.*/#define BOOT_TARGETS \"${rockchip_uboot_targets[*]}\"/" include/configs/rockchip-common.h
+	regular_git diff -u include/configs/rockchip-common.h || true
+}
+
 function post_family_tweaks__youyeetoo_yy3588_naming_audios() {
 	display_alert "$BOARD" "Renaming Youyeetoo YY3588 audios" "info"