mlxsw: spectrum_acl: Split region struct into region and vregion

Do the split of region struct so the new region struct is related to the
actual HW region, whereas vregion struct is a SW abstration of that.
This split prepares possibility for vregion to hold 2 HW regions which
is needed for region ERP rehash flow.

Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>