liquidio: avoided acquiring post_lock for data only queues

All control commands (soft commands) goes through only Queue 0
(control and data queue). So only queue-0 needs post_lock,
other queues are only data queues and does not need post_lock

Added a flag to indicate the queue can be used for soft commands.

If this flag is set, post_lock must be acquired before posting
a command to the queue.
If this flag is clear, post_lock is invalid for the queue.

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>