drm/amd/display: remove global optimize seamless boot stream count

[Why]
In following sequence driver will add counter twice on
same edp stream.
1. Boot into OS.
2. Set timing with edp only.
3. Set timing with edp and external monitor.
4. Set visibility on for edp.

Step 2 and 3 will add seamless boot counter twice and
subtract it once in step 4.

[How]
Remove global counter and calculate it is used.

Signed-off-by: Lewis Huang <Lewis.Huang@amd.com>
Reviewed-by: Martin Leung <Martin.Leung@amd.com>
Acked-by: Qingqing Zhuo <Qingqing.Zhuo@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>