drm/amd/display: Update bounding box values for DCN321

[Why&how]

Update bounding box values as per hardware spec

Fixes: 197485c6 ("drm/amd/display: Create dcn321_fpu file")
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>