Fix the MachineScheduler's logic for updating ready times for in-order.

Now the scheduler updates a node's ready time as soon as it is
scheduled, before releasing dependent nodes. There was a reason I
didn't do this initially but it no longer applies.

A53 is in-order and was running into an issue where nodes where added
to the readyQ too early. That's now fixed.

This also makes it easier for custom scheduling strategies to build
heuristics based on the actual cycles that the node was scheduled at.

The only impact on OOO (sandybridge/cyclone) is that ready times will
be slightly more accurate. I didn't measure any significant regressions.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210390 91177308-0d34-0410-b5e6-96231b3b80d8