nfp: release global resources only on the remove path

NFP app is currently shut down as soon as all the vNICs are gone.
This means we can't depend on the app existing throughout the
lifetime of the device.  Free the app only from PCI remove path.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Dirk van der Merwe <dirk.vandermerwe@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>