nfp: add support for .get_pauseparam()

Show correct pause frame parameters for nfp. These parameters cannot
be configured, so .set_pauseparam() is not implemented. With this
change:

 #ethtool --show-pause enp1s0np0
 Pause parameters for enp1s0np0:
 Autonegotiate:  off
 RX:             on
 TX:             on

Signed-off-by: Yinjun Zhang <yinjun.zhang@corigine.com>
Signed-off-by: Simon Horman <simon.horman@corigine.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/20220616133358.135305-1-simon.horman@corigine.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>