Claude review: drm/bridge: synopsys: dw-dp: Add Runtime PM support

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

Patch Review

Adds `dw_dp_runtime_suspend`/`dw_dp_runtime_resume` exported functions and sprinkles `ACQUIRE(pm_runtime_active_auto, pm)` / `pm_runtime_get_sync` / `pm_runtime_put_autosuspend` at appropriate points.

**Issue — no error checking on `clk_prepare_enable` in resume:**
```c
+int dw_dp_runtime_resume(struct dw_dp *dp)
+{
+	clk_prepare_enable(dp->apb_clk);
+	clk_prepare_enable(dp->aux_clk);
+	dw_dp_init_hw(dp);
+	return 0;
+}
```
`clk_prepare_enable()` can fail but return values are ignored. The suspend path also does unconditional `clk_disable_unprepare` without checking if they were successfully enabled.

**Issue — `pm_runtime_get_sync` in `atomic_enable` without error check:**
```c
+	pm_runtime_get_sync(dp->dev);
```
`pm_runtime_get_sync()` can return errors, and if it does, the function continues anyway. This should at minimum check the return value. The `ACQUIRE` guard pattern used elsewhere is actually better because it's scoped, but `atomic_enable` needs the device to stay active until `atomic_disable`, so the get/put pair is correct — just needs error handling.

---
Generated by Claude Code Patch Reviewer