nfp: add 'ethtool --identify' support

Add support for ethtool -p|--identify
by enabling blinking of the panel LED if supported by the NIC firmware.

Signed-off-by: Sixiang Chen <sixiang.chen@corigine.com>
Signed-off-by: Simon Horman <simon.horman@corigine.com>
Acked-by: Jakub Kicinski <kuba@kernel.org>
Link: https://lore.kernel.org/r/20220622083938.291548-1-simon.horman@corigine.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>