AMDGPU: Annotate implicitarg.ptr usage

We need to pass something to functions for this to work.
It isn't derivable just from the kernarg segment pointer
because the implicit arguments are placed after the
kernel arguments.

Also fixes missing test for the intrinsic.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@309398 91177308-0d34-0410-b5e6-96231b3b80d8
8 files changed