mlxsw: spectrum: qdiscs: Move qdisc's declarations to its designated file

Move all the qdisc related data from the spectrum.h to spectrum_qdisc.c.
Create an init and fini functions for the qdiscs.

Signed-off-by: Nogah Frankel <nogahf@mellanox.com>
Reviewed-by: Yuval Mintz <yuvalm@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>