AMDGPU: Fix emitting invalid workitem intrinsics for HSA

The AMDGPUPromoteAlloca pass was emitting the read.local.size
calls, which with HSA was incorrectly selected to reading from
the offset mesa uses off of the kernarg pointer.

Error on intrinsics which aren't supported by HSA, and start
emitting the correct IR to read the workgroup size
out of the dispatch pointer.

Also initialize the pass so it can be tested with opt, and
start moving towards not depending on the subtarget as an
argument.

Start emitting errors for the intrinsics not handled with HSA.

llvm-svn: 259297