Claude review: drm/msm/adreno: set cx_misc_mmio regardless of if platform has LLCC

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

Patch Review

This patch decouples the `cx_misc_mmio` mapping from LLCC slice availability. The key motivation is that Milos has no LLCC but still needs access to CX_MISC registers (for TCM retention, software fuses, etc.).

The approach is sound:
- MMU500 detection and `cx_misc_mmio` mapping are moved from `a6xx_llc_slices_init()` into `a6xx_gpu_init()`.
- The early-return guards in `a6xx_llc_activate()` and `a7xx_llc_activate()` are changed from checking `cx_misc_mmio` to checking whether LLC slices are available directly:

```c
-	if (IS_ERR(a6xx_gpu->cx_misc_mmio))
+	if (IS_ERR_OR_NULL(a6xx_gpu->llc_slice) && IS_ERR_OR_NULL(a6xx_gpu->htw_llc_slice))
```

This is safe because `a7xx_llc_activate()` (the path used for A8xx) does not use `cx_misc_mmio` — it only writes GPU registers via `gpu_write()` and calls `llcc_slice_activate()`. The `a6xx_llc_activate()` path does use `cx_misc_mmio` but only inside the `if (!a6xx_gpu->have_mmu500)` block, and for platforms that reach that code, `cx_misc_mmio` will be mapped (since `!have_mmu500` is one of the conditions for mapping it).

Already has Reviewed-by from both Konrad Dybcio and Akhil P Oommen. Looks correct.

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