drm/nouveau: rename "argv" to what it represents in *rm_{alloc, ctrl}_*()

The name "argv" has different meanings in different functions.

To improve the readability, it's better to refine it to a name that
reflects what it represents.

Rename "argv" to what it represents. Wrap the long container_of() into
to_payload_header() to denote a clear meaning and make checkpatch.pl
happy.

No functional change is intended.

Signed-off-by: Zhi Wang <zhiw@nvidia.com>
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20250124182958.2040494-6-zhiw@nvidia.com