net: dsa: sja1105: move sja1105_compose_gating_subschedule at the top

It turns out that sja1105_compose_gating_subschedule must also be called
from sja1105_vl_delete, to recalculate the overall tc-gate
configuration. Currently this is not possible without introducing a
forward declaration. So move the function at the top of the file, along
with its dependencies.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>