[OpenCL] Pipe type support

Summary:
Support for OpenCL 2.0 pipe type.
This is a bug-fix version for bader's patch reviews.llvm.org/D14441


Reviewers: pekka.jaaskelainen, Anastasia

Subscribers: bader, Anastasia, cfe-commits

Differential Revision: http://reviews.llvm.org/D15603

llvm-svn: 257254