[mlgo] Use LLVM_HAVE_TFLITE instead of LLVM_HAVE_TF_API

This patch replaces uses of LLVM_HAVE_TF_API with LLVM_HAVE_TFLITE in
a couple of CMakeLists.txt.

Now that 842b0d0f has landed,
we now have:

  LLVM_HAVE_TF_API is defined if and only if LLVM_HAVE_TFLITE
  evaluates to true

in the CMake variable world (assuming that you do not set
LLVM_HAVE_TF_API on the cmake invocation).

FWIW, the story is a little different in the C++ macro world, where:

  LLVM_HAVE_TF_API is defined if and only if LLVM_HAVE_TFLITE is
  defined

This is why edc83a15 consisted only of
mechanical replacements.

Differential Revision: https://reviews.llvm.org/D140061