mediatek: add Zyxel EX5601-T0 with uboot custom partition

mediatek: add Zyxel EX5601-T0 with uboot custom partition

The flash procedure is similar to the Xiaomi AX6000 router.

Load openwrt-mediatek-filogic-zyxel_ex5601-t0-ubootmod-initramfs-recovery.itb from original Zyxel U-Boot:

tftpboot openwrt-mediatek-filogic-zyxel_ex5601-t0-ubootmod-initramfs-recovery.itb
bootm 0x46000000
Load mtd-rw
insmod /lib/modules/$(uname -r)/mtd-rw.ko i_want_a_brick=1

Format ubi and create ubootenv partitions

ubidetach -p /dev/mtd5; ubiformat /dev/mtd5 -y; ubiattach -p /dev/mtd5
ubimkvol /dev/ubi0 -n 0 -N ubootenv -s 128KiB
ubimkvol /dev/ubi0 -n 1 -N ubootenv2 -s 128KiB
Copy openwrt-mediatek-filogic-zyxel_ex5601-t0-ubootmod-initramfs-recovery.itb to /tmp and create recovery partition.
If your recovery image is larger than 10MiB, size the recovery partition accordingly to make it fit.

ubimkvol /dev/ubi0 -n 2 -N recovery -s 10MiB
ubiupdatevol /dev/ubi0_2  openwrt-mediatek-filogic-zyxel_ex5601-t0-ubootmod-initramfs-recovery.itb
Copy preloader and uboot to /tmp and write them in the mtd

mtd write /tmp/openwrt-mediatek-filogic-zyxel_ex5601-t0-ubootmod-preloader.bin bl2
mtd write /tmp/openwrt-mediatek-filogic-zyxel_ex5601-t0-ubootmod-bl31-uboot.fip fip
Now write the firmware:
sysupgrade -n  /tmp/openwrt-mediatek-filogic-zyxel_ex5601-t0-ubootmod-squashfs-sysupgrade.itb

To create a correct BL2, I had to add a profile for 'spim:4k+256' as I could not find a way to value the variable 'NAND_TYPE'.

Features and fixes from hitech95 tree has been squashed, I'm attaching his commit message:

The Power LED was not working correctly and not reacting
 to the boot process and statuses.

The board has space (footprint) for an unpopulated Zigbee chip,
 while we dont know the device model having this chip populated
 we have to assure that the common dts doesnt enable
 interfaces that share pins with such device.

In this instance the PCIe and the uart1 and uart2 are disabled.
Some of the control PCIE pins seems to be used for the Zigbee chip,
 UART1 seems to be used as a flash port while UART2 should be the
 main comunication interface of Zigbee chip.

The Zigbee chip should be a EFR32MG21. But the pins used for UART
 seems to be not on standard PINS used by other adapters.
 So it cannot run firmwares shared on the web.
 But it should be possible to build a custom firmware with
 the corrtect pinmux.

This commit also contains the following squashed commit from hitech95
 - mediatek: fix sysupgrade for Zyxel EX7601-T0 ubootmod

Changes and fixes added in common board:
 - added aliases for boot status leds.
 - added aliases for the mac-label-device.
 - added pin claims for core features (MDIO and UART 0)
 - added default LEDs configuration (01_leds)
 - added default network configuration (02_network)
 - added missing kmod-usb3 module for USB3
 - fixed LED names
 - fixed reset pin for SLIC chip
 - removed unused pinmux configurations and devices
 - fix LAN (switch) port numbering
 - using nvmem cells for wifi eeprom, dropping deprecated "mediatek,mtd-eeprom"
 - proper factory partition and mac address handling
 - cleaned up spi_nand sections and partition

Changes and fixxes added in stock layout:
 - added NMBM, if u-boot has it, the kernel must be informed.

Co-authored-by: Nicolò Veronese <nicveronese@gmail.com>
Co-developed-by: Nicolò Veronese <nicveronese@gmail.com>
Signed-off-by: Nicolò Veronese <nicveronese@gmail.com>
Signed-off-by: Valerio 'ftp21' Mancini <ftp21@ftp21.eu>
(cherry picked from commit b5df398a36f153f036c0a5ff9b221abb0f6f240a)