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

This reverts commit 4541ea81.

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>