event/dlb: add dequeue and its burst variants

event/dlb: add dequeue and its burst variants

Add support for dequeue, dequeue_burst, ...

DLB does not currently support interrupts, but instead uses
umonitor/umwait if supported by the processor. This allows
the software to monitor and wait on writes to a cache-line.

DLB supports normal and sparse cq mode. In normal mode the
hardware will pack 4 QEs into each cache line. In sparse cq
mode, the hardware will only populate one QE per cache line.
Software must be aware of the cq mode, and take the appropriate
actions, based on the mode.

Signed-off-by: Timothy McDaniel <timothy.mcdaniel@intel.com>
Reviewed-by: Gage Eads <gage.eads@intel.com>