drm/amdgpu: remove unnecessary header include

amdgpu.h is included in kfd_priv.h

Signed-off-by: Hawking Zhang <Hawking.Zhang@amd.com>
Reviewed-by: John Clements <John.Clements@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>