drm/amd/powerplay: Partially revert changes and fix smu7_notify_smc_display()

This partially reverts 0b6b4cbf77c995a34a4ec3d705a636434dadc51a and fixes
the noise issues on Tonga.

Signed-off-by: Tom St Denis <tom.stdenis@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>