[mlir][llvm] Define annotation intrinsics

Define `llvm.intr.var.annotation`, `llvm.intr.ptr.annotation` and
`llvm.intr.annotation` in the llvm dialect as `llvm.var.annotation`,
`llvm.ptr.annotation` and `llvm.annotation` counterparts.

Signed-off-by: Victor Perez <victor.perez@codeplay.com>

Differential Revision: https://reviews.llvm.org/D154842