drm/amd/powerplay: bypass dpm_context null pointer check guard for some smu series

For now APU has no smu_dpm_context structure for containing default/current related dpm tables,
thus will needn't initialize smu_dpm_context to aviod APU null pointer issue.

Signed-off-by: Prike Liang <Prike.Liang@amd.com>
Reviewed-by: Kevin Wang <kevin1.wang@amd.com>
Reviewed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>