nfp: reorganize the app table

The app table is an unordered array right now.  We have to search
apps by ID.  It also makes it harder to fall back to core NIC if
advanced functions are not compiled into the kernel (e.g. eBPF).
Make the table keyed by app id.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>