tests/amdgpu: fix uvd enc data corruption issue

In uvd encode parameter package, parameters input_pic_luma_pitch and
input_pic_chroma_pitch should be picture width align with hardware alignment.
The hardware alignment is 16 for amdgpu family earlier than AMDGPU_FAMILY_AI,
and 256 for later than and including AMDGPU_FAMILY_AI.

Signed-off-by: James Zhu <James.Zhu@amd.com>
Reviewed-by: Leo Liu <leo.liu@amd.com>