nfp: convert all RTsym users to use new read/write helpers

Convert all users of RTsym to the new set of helpers which
handle all targets correctly.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Francois H. Theron <francois.theron@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>