nfp: convert existing RTsym helpers to full target decoding

Make nfp_rtsym_{read,write}_le() and nfp_rtsym_map() use the new
target resolution helpers to allow accessing in-cache symbols.

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>