drm/amd/display: Use active + border for bw validation

When doing SLS, KMD gives us clipped v_addressable with
border. This results in bw validation failure.

Signed-off-by: Eric Yang <Eric.Yang2@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Harry Wentland <Harry.Wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>