Banana Pi M2 Ultra (R40): fails to boot with CURRENT kernel, OK on LEGACY

Split out from the sunxi u-boot v2026.07 migration (#10069).

## Summary
**Banana Pi M2 Ultra** (Allwinner **R40**, `BOARDFAMILY=sun8i`, `KERNEL_TARGET=current,edge,legacy`) **boots fine on the LEGACY kernel** but **fails to boot on the CURRENT kernel**.

This is a **kernel-branch issue, not u-boot** — it was found while validating the sunxi u-boot bump to v2026.07-rc4 (#10069), and the u-boot port itself is confirmed working (the board boots on legacy with the new u-boot). So it should be tracked/fixed independently of the u-boot migration.

## Status
- u-boot v2026.07-rc4 (sunxi bump, #10069): ✅ builds + boots (legacy kernel)
- current kernel: ❌ does not boot
- legacy kernel: ✅ boots fine

## Needed to diagnose
- Serial console log of the **current**-kernel boot up to where it stops (does it reach `Starting kernel`? hang point / panic?).
- Confirm whether `edge` behaves like `current` or like `legacy`.

## Notes
R40 (sun8iw11) current/edge kernel support is the likely area — DT, clocks, or a driver regression vs the legacy branch. Not a regression from the u-boot work.

cc: ref #10069

Start by obtaining a serial console log for the CURRENT-kernel boot and identify whether it reaches “Starting kernel” or where it stops. Compare CURRENT, EDGE, and LEGACY behavior for the Banana Pi M2 Ultra, then investigate the R40 current/edge support area mentioned in the issue, including DT, clocks, and driver regressions. Done means the boot failure has a confirmed cause and the affected kernel branch boots reliably.

Written by the indexing model from the issue text.