Interprocedural Register Allocation (IPRA): add a Transformation Pass

Adds a MachineFunctionPass that scans the body to find calls, and
update the register mask with the one saved by the
RegUsageInfoCollector analysis in PhysicalRegisterUsageInfo.

Patch by Vivek Pandya <vivekvpandya@gmail.com>

Differential Revision: http://reviews.llvm.org/D21180

llvm-svn: 272414