Claude review: drm/panthor: Use a local iomem base for MMU AS registers

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

Patch Review

The rename from `MMU_BASE` to `MMU_AS_BASE` and the change of `MMU_AS(as)` from `(MMU_BASE + ((as) << MMU_AS_SHIFT))` to `((as) << MMU_AS_SHIFT)` is correct. With `mmu->iomem = ptdev->iomem + MMU_AS_BASE`, all AS register accesses compute the correct absolute offset.

The MMU IRQ accesses via `mmu->irq.iomem` (base 0x2000) with generic `INT_CLEAR` etc. are correct.

The removal of absolute `MMU_INT_RAWSTAT`/`MMU_INT_CLEAR`/etc. defines is correct -- these are now accessed through the generic `INT_*` offsets.

No issues.

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**Summary of required fixes before merging:**

| Severity | Patch | Issue |
|----------|-------|-------|
| Critical | 6 | `panthor_hw.c` reads PWR_*_PRESENT with now-relative offsets via `ptdev->iomem` -- wrong registers |
| Build break | 4 | `GPU_CONTROL_BASE` used before defined (bisection failure) |
| Bug | 3 | Function names `panthor_gpu_get_timestap*` misspelled (missing 'm') |
| Minor | 3 | Stray `\` line continuation in `panthor_fw_ring_csg_doorbells` |
| Minor | 4 | Generic `INT_RAWSTAT`/`INT_CLEAR`/etc. macro names risk collisions |
| Minor | 2 | Original copyright attributions dropped from split headers |

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