kernel: Add method to dequeue from a dlist

Dequeuing from a doubly linked list is similar to removing an item
except that it does not re-initialize the dequeued node.

This comes in handy when sorting a doubly linked list (where the
node gets removed and re-added). In that circumstance, re-initializing
the node is required. Furthermore, the compiler does not always
'understand' this. Thus, when performance is critical, dequeuing
may be preferred to removing.

Signed-off-by: Peter Mitsis <peter.mitsis@intel.com>