sched/fair: bonus vruntime for task boost 3

When task boost with special value 3 also have vruntime
bonus to run faster.

Change-Id: I7da2dd985a961671b27036a0d5b13cb79480c933
Signed-off-by: Maria Yu <aiquny@codeaurora.org>
[satyap@codeaurora.org: fix compilation issues with User Mode Linux]
Signed-off-by: Satya Durga Srinivasu Prabhala <satyap@codeaurora.org>