nfp: allow multi-stage NSP configuration

nfp: allow multi-stage NSP configuration

NSP commands may be slow to respond, we should try to avoid doing
a command-per-item when user requested to change multiple parameters
for instance with an ethtool .set_settings() command.

Introduce a way of internal NSP code to carry state in NSP structure
and add start/finish calls to perform the initialization and kick off
of the configuration request, with potentially many parameters being
modified in between.

nfp_eth_set_mod_enable() will make use of the new code internally,
other "set" functions to follow.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>