mediatek: add support for BananaPi BPI-R4 board

Hardware
--------
SOC:    MediaTek MT7988A (4x Cortex-A73)
RAM:    4 GiB DDR4
Flash:  128 MiB Winbond SPI-NAND
MMC:    8 GiB eMMC *or* microSD (cannot be used both)
ETH:    4x 1GE (1x WAN, 3x LAN)
        2x SFP+ (10G, 5G, 2.5G, 1G)
USB:    on-board USB 3.2 4-port hub
        1x USB 3.2 port (type A connector)
        1x M.2 for 4G/5G modem
        2x mPCIe for additional modems
WiFi:   optional MediaTek MT7996 Wi-Fi 7 module
        (using 2x PCIe gen3 x2 on the mPCIe slots and 12V power)

Installation
------------
1. Decompress and write the sdcard image to a micro SD card and use that
to boot the R4 (both dip switches in upper position).

2. Use the bootloader menu accessible via the serial console to install
to SPI-NAND.

3. Switch to boot from SPI-NAND and install to eMMC.

Known issues
------------
 - The RST button is hard-wired to the SoC reset and can't be read
   from software. This can be changed by modifying the board (ie.
   moving a 0-ohm resistor). However, in order to maintain compatibility
   with the board as it comes from factory the button isn't used by
   OpenWrt and the WPS button is used as factory/reset button instead.

 - various small things still need to be fixed in DT

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

target/linux/mediatek/filogic/base-files/lib/upgrade/platform.sh

@@ -1,4 +1,5 @@
 REQUIRE_IMAGE_METADATA=1
+RAMFS_COPY_BIN='fitblk'
 
 asus_initial_setup()
 {
@@ -59,6 +60,21 @@ xiaomi_initial_setup()
 	esac
 }
 
+platform_get_bootdev() {
+	local rootdisk="$(cat /sys/firmware/devicetree/base/chosen/rootdisk)"
+	local handle bootdev
+	for handle in /sys/class/block/*/of_node/phandle /sys/class/block/*/device/of_node/phandle; do
+		[ ! -e "$handle" ] && continue
+		if [ "$rootdisk" = "$(cat $handle)" ]; then
+			bootdev="${handle%/of_node/phandle}"
+			bootdev="${bootdev%/device}"
+			bootdev="${bootdev#/sys/class/block/}"
+			echo "$bootdev"
+			break
+		fi
+	done
+}
+
 platform_do_upgrade() {
 	local board=$(board_name)
 
@@ -99,6 +115,21 @@ platform_do_upgrade() {
 			;;
 		esac
 		;;
+	bananapi,bpi-r4)
+		[ -e /dev/fit0 ] && fitblk /dev/fit0
+		[ -e /dev/fitrw ] && fitblk /dev/fitrw
+		bootdev="$(platform_get_bootdev)"
+		case "$bootdev" in
+		mmcblk*)
+			EMMC_KERN_DEV="/dev/$bootdev"
+			emmc_do_upgrade "$1"
+			;;
+		ubiblock*)
+			CI_KERNPART="fit"
+			nand_do_upgrade "$1"
+			;;
+		esac
+		;;
 	cmcc,rax3000m)
 		case "$(cmdline_get_var root)" in
 		/dev/mmc*)
@@ -175,6 +206,7 @@ platform_check_image() {
 
 	case "$board" in
 	bananapi,bpi-r3|\
+	bananapi,bpi-r4|\
 	cmcc,rax3000m)
 		[ "$magic" != "d00dfeed" ] && {
 			echo "Invalid image type."
@@ -201,6 +233,13 @@ platform_copy_config() {
 			;;
 		esac
 		;;
+	bananapi,bpi-r4)
+		case "$(platform_get_bootdev)" in
+		mmcblk*)
+			emmc_copy_config
+			;;
+		esac
+		;;
 	acer,predator-w6|\
 	glinet,gl-mt2500|\
 	glinet,gl-mt6000|\