Claude review: drm/msm/adreno: use qcom_ubwc_version_tag() helper

[Claude Code Review Bot <claude-review@example.com>]

Patch Review

Replaces hardcoded `mode` values in `a8xx_set_ubwc_config` with `qcom_ubwc_version_tag(cfg)` and removes the inline version ladder from `msm_mdss_setup_ubwc_v6`.

**Potential bug in MDSS**: The MDSS change removes the `ver` variable and the `writel_relaxed(ver, ...)` to `REG_MDSS_UBWC_CTRL_2`:
```c
-	writel_relaxed(ver, msm_mdss->mmio + REG_MDSS_UBWC_CTRL_2);
 	writel_relaxed(prediction_mode, msm_mdss->mmio + REG_MDSS_UBWC_PREDICTION_MODE);
```

This looks like it drops the UBWC_CTRL_2 register write entirely. This register was being written in both the old `msm_mdss_setup_ubwc_dec_40` and `msm_mdss_setup_ubwc_dec_50` paths. If this is intentional, the commit message should explain why. If not, this is a regression -- the line should be:
```c
writel_relaxed(qcom_ubwc_version_tag(data), msm_mdss->mmio + REG_MDSS_UBWC_CTRL_2);
```

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