stm32: add new stm32 target

New stm32 target introduces support for stm32mp1 based devices.
For now it includes an initial support of the STM32MP135F-DK device.
The specifications bellow only list supported features.

Specifications
--------------

SOC: STM32MP135FAF7
RAM: 512 MiB
Storage: SD Card
Ethernet: 2x 100 Mbps
Wireless: 2.4GHz Cypress CYW43455 (802.11b/g/n)
LEDs: Heartbeat (Blue)
Buttons: 1x Reset, 1x User (USER2)
USB: 4x 2.0 Type-A

Signed-off-by: Thomas Richard <thomas.richard@bootlin.com>
Link: https://github.com/openwrt/openwrt/pull/16716
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>

target/linux/stm32/base-files/lib/preinit/79_move_config

@@ -0,0 +1,15 @@
+
+move_config() {
+	. /lib/upgrade/common.sh
+	. /lib/upgrade/platform.sh
+
+	if export_bootdevice && export_partdevice partdev 4; then
+		mount -t ext4 -o rw,noatime "/dev/$partdev" /mnt
+		if [ -f "/mnt/$BACKUP_FILE" ]; then
+			mv -f "/mnt/$BACKUP_FILE" /
+		fi
+		umount /mnt
+	fi
+}
+
+boot_hook_add preinit_mount_root move_config