drm/amd/display: MALL SS calculations should iterate over all pipes for cursor

[Description]
MALL SS allocation calculations should iterate over all pipes to determine the
the allocation size required for HW cursor.

Reviewed-by: Alvin Lee <Alvin.Lee2@amd.com>
Acked-by: Jasdeep Dhillon <jdhillon@amd.com>
Signed-off-by: Dillon Varone <Dillon.Varone@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>