nfp: bpf: move program prepare and free into offload.c

Most of offload/translation prepare logic will be moved to
offload.c.  To help git generate more reasonable diffs
move nfp_prog_prepare() and nfp_prog_free() functions
there as a first step.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>