Base support for Inteno XG6846

These patches have been cooking for some time, let's
get them moving.

The idea is to merge this base so we have base support
for the target and then try to work out remaining issues
such as the LED handling.

To: openwrt-devel@lists.openwrt.org
To: Paul D <newtwen@gmail.com>
To: Álvaro Fernández Rojas <noltari@gmail.com>
To:
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
---
Changes in v3:
- EDITME: describe what is new in this series revision.
- EDITME: use bulletpoints and terse descriptions.
- Link to v2: https://lore.kernel.org/r/20240425-xg6846-base-v2-0-77bcdab747e9@linaro.org

Changes in v2:
- Include U-Boot for BMIPS patch (2024.04)
- Separate patch to activate U-Boot with the target.
- Use a kmod for the Marvell switch to hold down the footprint
  of the generic BCM6328 support.
- Link to v1: http://lists.openwrt.org/pipermail/openwrt-devel/2023-August/041387.html

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