drm/amdgpu: Clear build undefined warning

Add amdgpu_amdkfd_arcturus_get_functions stub when
CONFIG_HSA_AMD is undefinded.

Signed-off-by: James Zhu <James.Zhu@amd.com>
Reviewed-by: Yong Zhao <Yong.Zhao@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>