Quick: In GVN, apply modifications early if outside loop.

To improve GVN performance, apply modifications to blocks
outside loops during the initial convergence phase. During
the post processing phase, apply modifications only to the
blocks belonging to loops.

Also clean up the check whether to run the LVN and add the
capability to limit the maximum number of nested loops we
allow the GVN to process.

Change-Id: Ie7f1254f91a442397c06a325d5d314d8f58e5012