The power smu7 powerplay code is much more robust and has
been the default for a while now.  Remove the old code.
Acked-by: NChristian König <christian.koenig@amd.com>
Reviewed-by: NEvan Quan <evan.quan@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>