This can solve the path problem when compile amdgpu with DKMS.

v2: agd: rebase on current drm-next
Signed-off-by: Jammy Zhou <Jammy.Zhou@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>