sfc: Record [rt]x_dpcpu_fw_id in EF10 nic_data

The (future) code to add/remove vswitches and vports will be
dependent on the firmware variant.
To simplify the checking of the firmware variant, record
values for rx_dpcpu_fw_id and tx_dpcpu_fw_id in EF10 nic_data.

There was only one place where this was previously used:
efx_mcdi_print_fwver() in ethtool.c.
The MC_CMD_GET_CAPABILITIES can be replaced and the values from
nic_data used instead.

Note that the printing of "?" if the MC command fails or if the
outlength is incorrect no longer apply, because errors are returned
in efx_ef10_init_datapath_caps() in both of these cases.

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