[OpenCL] Refine OpenCLImageAccessAttr to OpenCLAccessAttr

Summary:
OpenCL access qualifiers are now not only used for image types, refine it to avoid misleading,

Add semacheck for OpenCL access qualifier as well as test caees.

Reviewers: pekka.jaaskelainen, Anastasia, aaron.ballman

Subscribers: aaron.ballman, cfe-commits

Differential Revision: http://reviews.llvm.org/D16040

llvm-svn: 261961