drm/amdgpu/swSMU: correct the bootup power source for Navi1X (v2)

PMFW may boots those ASICs with DC mode. Need to set it back
to AC mode.

v2: split from Evan's original patch (Alex)

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


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