Claude review: drm/ast: Move 32-bit register-access helpers to ast_drv.{c, h}

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

Patch Review

Good refactoring. The reimplementation of `__ast_mindwm`/`__ast_moutdwm` with properly named sub-helpers (`__ast_selseg`, `__ast_rdseg32`, `__ast_wrseg32`) is cleaner and adds `cpu_relax()` to the busy-wait loop, which the original lacked.

One minor observation: the `__ast_selseg` helper calls `cpu_relax()` before the first read in the polling loop, whereas the original code did not relax at all. This is strictly better but moves from a tight spin to a relaxed spin.

The P2A register constants are well-defined:
```c
#define AST_REG_P2A00           AST_REG_P2A(0xf000)
#define AST_REG_P2A04           AST_REG_P2A(0xf004)
```

Note: The naming `P2A00` for offset `0xf000` is a bit confusing - the "00" suffix doesn't correspond to the offset. This follows the hardware register naming convention (P2A register 00), but a comment might help.

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