drm/amdgpu/powerplay/smu10: add support for gpu busy query (v2)

Was added in newer versions of the firmware.  Add support
for it.

v2: return an error in SMU error, drop needless break.

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