Add support for rk3566-box-demo

This is a rk3566 tv box evaluation demo board.

Specification:
- Rockchip RK3566
- DDR4 4GB
- TF sd scard slot
- eMMC
- AP6398S for WiFi + BT
- Gigabit ethernet
- HDMI out
- USB HOST 2.0 x 2
- USB 3.0 x 1
- USB OTG 2.0  x 1
- 12V DC Power supply

Signed-off-by: Andy Yan <andyshrk@gmail.com>

config/boards/rk3566-box-demo.csc

@@ -0,0 +1,32 @@
+# Rockchip RK3566 with 4GB DDR HDMI USB3 WIFI GMAC
+BOARD_NAME="RK3566 BOX DEMO"
+BOOT_SOC="rk3566"
+BOARDFAMILY="rk35xx"
+BOARD_MAINTAINER="andyshrk"
+BOOTCONFIG="generic-rk3568_defconfig"
+KERNEL_TARGET="current,edge"
+FULL_DESKTOP="yes"
+BOOT_LOGO="desktop"
+BOOT_FDT_FILE="rockchip/rk3566-box-demo.dtb"
+BOOT_SCENARIO="spl-blobs"
+IMAGE_PARTITION_TABLE="gpt"
+
+# Mainline U-Boot
+function post_family_config__rk3566_box_demo_use_mainline_uboot() {
+	display_alert "$BOARD" "Using mainline U-Boot for $BOARD / $BRANCH" "info"
+
+	declare -g BOOTSOURCE="https://github.com/u-boot/u-boot.git"
+	declare -g BOOTBRANCH="tag:v2025.10"
+	declare -g BOOTPATCHDIR="v2025.10"
+	# Don't set BOOTDIR, allow shared U-Boot source directory for disk space efficiency
+
+	declare -g UBOOT_TARGET_MAP="BL31=${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
+	}
+}