Move setting the display state out of the critical section.

Setting the display power state currently happens while holding the
display manager lock.  This change moves it out of the lock to
ensure other services don't get stuck for several hundred
milliseconds.

Unfortunately, surface flinger ends up stalled a little later
so this only solves part of the problem.

Bug: 17623774
Change-Id: I201137c5e7f82c776f28a436845fcf3191fd0ca5