sfc: create vports for VFs and assign random MAC addresses

The parent PF creates vports for all its child VFs and adds MAC
addresses to these.  When the VF driver loads, it can make an MCDI
call to get the MAC address that the parent PF assigned it.

The parent PF also assigns a mac address to its own vport because
implicit creation of a vAdaptor will only work on evb ports with
MAC addresses assigned.

The vport MAC address needs to be stored in the PF's nic_data
struct as it can later be changed on the vadaptor (and its net_dev
struct). When removing a vport the original MAC address must be
deleted.

A new flag is needed in the VF data structure to identify whether
a vport has been assigned to the VF.  This is to determine whether
it needs to be un-assigned before freeing the vport.  Also,
attempting to un-assign a vport which is not assigned will result
in an EALREADY error.

Signed-off-by: Shradha Shah <sshah@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>