drm/amdgpu: Remove duplicated includes

Remove duplicated includes in amdgpu_amdkfd_gpuvm.c and amdgpu_ttm.c.
Resolves checkincludes message.

Signed-off-by: GUO Zihua <guozihua@huawei.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>