mlxsw: spectrum_acl: Split chunk struct into chunk and vchunk

Do the split of chunk struct so the new chunk struct is related to the
actual HW chunk (differs between Spectrum and Spectrum-2),
whereas vchunk struct is a SW abstraction of that. This split
prepares possibility for vchunk to hold 2 HW chunks 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>