drm/amd/pm: Add debug prints

Add prints where there are none and none are printed in the callee.

Remove the word "previous" from comment and print to make it shorter and
avoid confusion in various prints.

Cc: Alex Deucher <Alexander.Deucher@amd.com>
Signed-off-by: Luben Tuikov <luben.tuikov@amd.com>
Reviewed-by: Alex Deucher <Alexander.Deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>