R600/SI: add sample and image intrinsics exposing all instruction fields

We need the intrinsics with offsets, so why not just add them all.
The R128 parameter will also be useful for reducing SGPR usage.
GL_ARB_image_load_store also adds some image GLSL modifiers like "coherent",
so Mesa will probably translate those to slc, glc, etc.

When LLVM 3.5 is released, I'll switch Mesa to these new intrinsics.

llvm-svn: 212830