nfp: bpf: require seamless reload for program replace

Firmware supports live replacement of programs for quite some
time now.  Remove the software-fallback related logic and
depend on the FW for program replace.  Seamless reload will
become a requirement if maps are present, anyway.

Load and start stages have to be split now, since replace
only needs a load, start has already been done on add.

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>