block: Expose kblock_schedule_delayed_work()

This function is exported in blk-core.c to be used in other modules
but it's definition in h file is missing.

Change-Id: I3374d97774adf06c1f93e40f1d5e1daefb983571
Signed-off-by: Tatyana Brokhman <tlinder@codeaurora.org>
(cherry picked from commit 87c7500d26ddddf2851bbe65190f5d8970b0346d)
sched: Skip looking at skip if next or last is set

pick_next_entity() prefers next, then last. However code checks if the
left entity can be skipped even if next / last is set.

Check if left entity should be skipped only if next/last is not set.

Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>