drm/amd/display: calculate final viewport before TAP optimization

Viewport size excess surface size observed sometime with some timings or
resizing the MPO video window to cause MPO unsupported. Calculate final
viewport size first with a 100x100 dummy viewport to get the max TAP
support and then re-run final viewport calculation if TAP value changed.
Removed obsolete preliminary viewport calculation for TAP validation.

Reviewed-by: Dmytro Laktyushkin <dmytro.laktyushkin@amd.com>
Signed-off-by: Yihan Zhu <Yihan.Zhu@amd.com>
Signed-off-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>