drm/amdgpu: add more debug friendly prompts

Large piece of codes share one error prompt. That
is not friendly for debugging.

Signed-off-by: Evan Quan <evan.quan@amd.com>
Reviewed-by: Feifei Xu <Feifei.Xu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>