drm/amd/powerplay: Move smu7*.h from amdgpu to powerplay.

BugLink: http://bugs.launchpad.net/bugs/1546572

Move smu7.h, smu7_discrete.h and smu7_fusion.h from amdgpu to powerplay.
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: yanyang1 <young.yang@amd.com>
(cherry picked from commit 7ff1d70a)
Signed-off-by: Alberto Milone <alberto.milone@canonical.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>