Revert "drm/[radeon|amdgpu]: Replace one-element array and use struct_size() helper"

This reverts commit 4541ea81

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This changes structs used by the hardware and breaks dpm on some cards.

Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>