drm/amdgpu/swSMU: handle DC controlled by GPIO for navi1x

Check the platform caps in the vbios pptable to decide
whether to enable automatic AC/DC transitions.

Bug: https://gitlab.freedesktop.org/drm/amd/issues/1043


Reviewed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>