drm/amd/pm: zero unused SMU argument registers

drm/amd/pm: zero unused SMU argument registers

SMU messages may use fewer arguments than the available argument registers,
the previous code only wrote used registers and left the rest unchanged,
so stale values from a prior message could persist.

Write all argument registers for each message and zero the unused tail
to keep command arguments deterministic and avoid unintended carry-over.

Signed-off-by: Yang Wang <kevinyang.wang@amd.com>
Reviewed-by: Asad Kamal <asad.kamal@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit e03b635f61f77ebd5107ef82f48e3221cb695856)