drm/amd/display: wait for the whole frame after global unlock

[why]
The current code will not wait for the entire frame
 after global unlock.
This causes dsc dynamic target bpp update corruption when
there is a surface update immediately happens after this.

[how]
Wait for the entire whole frame after unlock before continuing
the rest of stream and surface update.

Signed-off-by: Wenjing Liu <Wenjing.Liu@amd.com>
Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>