[Why]
idle optimization was being disabled after commit.

[How]
check vblank count for display off and enable idle optimization based on this count.
Also,check added to ensure vblank count does not decrement, when count reaches 0.
Reviewed-by: NKenneth Feng <kenneth.feng@amd.com>
Signed-off-by: NBindu Ramamurthy <bindu.r@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>