The tflm tool registered DEPTHWISE_CONV_2D in nuttx-apps#3773, but the
docs still listed eight operators. Document the unused -C compile path,
that the sim helper uses heap I/O, and the pinned TFLM/CMSIS/NNABLA
versions. Add missing gemmlowp, KissFFT, Ruy, and FlatBuffers pages,
document the AI-engine character driver, and wire it into CMake.
Signed-off-by: Abhishek Mishra <mishra.abhishek2808@gmail.com>