sfc: Store vf_index in nic_data for Ef10.

Added function efx_ef10_get_vf_index to store the vf_index
in nic_data during probe

vf_index is needed in future patches to access a particular
VF in the VF data structure.

Moved efx_ef10_probe_pf and efx_ef10_probe_vf in order to
used efx_ef10_remove

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