eventdev: define default value for dequeue timeout

Defining the value 0 as default value for dequeue timeout
will help the application reduce the configuration setup
if the application is interested only in default
timeout value.

removed "min_dequeue_limit" negative testcase as
min_dequeue_limit value could be zero(which is
default timeout now) if driver has
dev_info->min_dequeue_timeout_ns  = 1.

Signed-off-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>