liquidio: Simplified napi poll

1) Moved interrupt enable related code from octeon_process_droq_poll_cmd()
   to separate function octeon_enable_irq().
2) Removed wrapper function octeon_process_droq_poll_cmd(), and directlyi
   using octeon_droq_process_poll_pkts().
3) Removed unused macros POLL_EVENT_XXX.

Signed-off-by: Intiyaz Basha <intiyaz.basha@cavium.com>
Signed-off-by: Felix Manlunas <felix.manlunas@cavium.com>
Signed-off-by: David S. Miller <davem@davemloft.net>