sfc: Own header for nic-specific sriov functions, single instance of netdev_ops and sriov removed from Falcon code

By putting all the efx_{siena,ef10}_sriov_* declarations in
{siena,ef10}_sriov.h, ensure they cannot be called from nic-generic code.
Also fixes up an instance of this, where mcdi.c was calling
efx_siena_sriov_flr.

The single instance of netdev_ops should call general high level
functions that can then call something adapter specific in efx_nic_type.
We should only do adapter specialisation via efx_nic_type.

Removal of sriov functionality from the Falcon code means that tests
are needed for the presence of some callbacks.
Signed-off-by: NShradha Shah <sshah@solarflare.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>