realtek: add support for Linksys LGS328MPCv2

realtek: add support for Linksys LGS328MPCv2

Hardware specification
----------------------

* RTL9301 SoC, 1 MIPS 34KEc core @ 800MHz
* 512MB DRAM
* 2MB NOR Flash
* 128MB NAND Flash
* 24 x 10/100/1000BASE-T ports with PoE+
* 4 x 10G SFP+ ports
* Power LED, Fault LED, PoE Max LED, LAN Mode LED, PoE Mode LED
* Reset button and LED Mode button on front panel
* LM63 Fan Controller
* UART (115200 8N1) via RJ45
* PSE: Nuvoton M0516LDE via I2C + 3x RTL8238B (not supported yet)

Installation using serial interface
-----------------------------------

1. Press "a" "c" "p" during message "Enter correct key to stop autoboot"
2. Start network "rtk network on"
3. Load image "tftpboot <TFTP IP>:openwrt-realtek-rtl930x_nand-linksys_lgs328mpc-v2-initramfs-kernel.bin"
4. Boot image "bootm"
5. Switch to first bootpartition "fw_setsys bootpartition 0"
6. Download sysupgrade "scp <IP>:openwrt-realtek-rtl930x_nand-linksys_lgs328mpc-v2-squashfs-sysupgrade.bin /tmp/."
7. Install sysupgrade "sysupgrade /tmp/openwrt-realtek-rtl930x_nand-linksys_lgs328mpc-v2-squashfs-sysupgrade.bin"

Installation using OEM webinterface
-----------------------------------

This is not possible because the OpenWrt NAND Flash layout is different
from the vendor layout. To be precise. Vendor uses:

- 64 MB vendor UBI root_data
- 32 MB vendor kernel+root 1 (~19 MB used)
- 32 MB vendor kernel+root 2 (~19 MB used)

OpenWrt uses:

- 64 MB vendor UBI (not touched)
- 10 MB OpenWrt kernel
- 22 MB Openwrt mtd-concat UBI
- 23 MB vendor kernel 2 (space reduced, vendor data unchanged)
- 09 MB OpenWrt mtd-concat UBI

Dual-boot with stock firmware using writable u-boot-env
-------------------------------------------------------

From stock to OpenWrt / primary image 1 (CLI as admin):
   - > boot system image1
   - > reboot

From OpenWrt to stock / boot image 2: (shell as root)
   - # fw_setsys bootpartition 1
   - # reboot

Debrick using serial interface
------------------------------

1. Press "a" "c" "p" during message "Enter correct key to stop autoboot"
2. Load vendor image with "upgrade runtime <TFTP IP>:LGS328xxxxx.imag"
3. switch to primary partition "setsys bootpartition 0"
4. safe config "savesys"

MAC Address Source
------------------

The MAC address for this device is coming from the u-boot-env ethaddr cell.

Further documentation
---------------------
See https://openwrt.org/toh/linksys/lgs352c

Signed-off-by: Jan-Henrik Bruhn <git@jhbruhn.de>
Link: https://github.com/openwrt/openwrt/pull/23466
Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>