[SystemZ] Recognize Load On Condition Immediate (LOCHI/LOGHI) opportunities

Summary: Add support for the z13 instructions LOCHI and LOCGHI which
conditionally load immediate values.  Add target instruction info hooks so
that if conversion will allow predication of LHI/LGHI.

Author: RolandF

Reviewers: uweigand

Subscribers: zhanjunl

Commiting on behalf of Roland.

Differential Revision: http://reviews.llvm.org/D22117

llvm-svn: 275086