nfp: nsp: add support for optional hwinfo lookup

There are cases where we want to read a hwinfo entry from the NFP, and
if it doesn't exist, use a default value instead.

To support this, we must silence warning/error messages when the hwinfo
entry doesn't exist since this is a valid use case. The NSP command
structure provides the ability to silence command errors, in which case
the caller should log any command errors appropriately. Protocol errors
are unaffected by this.

Signed-off-by: Dirk van der Merwe <dirk.vandermerwe@netronome.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>