mlxsw: spectrum_router: Introduce per-ASIC XM initialization

During the router init flow, call into XM code and initialize couple of
items needed for XM functionality:

1) Query the capabilities and sizes. Check the XM device id.
2) Initialize the M-value. Note that currently the M-value is set fixed
   to 16 for IPv4. In future this may change to better cover the actual
   inserted routes.

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>