IR printing improvement for loop passes - handle -print-module-scope

Summary:
Adding support for -print-module-scope similar to how it is
being done for function passes. This option causes loop-pass printer
to emit a whole-module IR instead of just a loop itself.

Reviewers: sanjoy, silvas, weimingz

Reviewed By: sanjoy

Subscribers: apilipenko, skatkov, llvm-commits

Differential Revision: https://reviews.llvm.org/D40247

llvm-svn: 319566