Claude review: misc: fastrpc: Move fdlist to invoke context structure

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

Patch Review

**Assessment: Looks good with one minor observation.**

This patch moves the `fdlist` pointer from being recalculated in `fastrpc_put_args()` to being computed once in `fastrpc_get_args()` and stored in the context structure. This is a clean refactoring.

The original `fastrpc_put_args()` computed the fdlist as:
```c
fdlist = (uint64_t *)(pages + inbufs + outbufs + handles);
```
The new code in `fastrpc_get_args()` computes:
```c
ctx->fdlist = (u64 *)(pages + ctx->nscalars);
```

Since `ctx->nscalars = inbufs + outbufs + handles`, these are equivalent. The patch also removes `outbufs`, `handles`, `list`, and `pages` local variables from `fastrpc_put_args()` that are no longer needed.

**No issues found.**

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