Generate dealloc's for alloc's of pipeline-data-transfer

- for the DMA transfers being pipelined through double buffering, generate
  deallocs for the double buffers being alloc'ed

This change is along the lines of cl/233502632. We initially wanted to experiment with
scoped allocation - so the deallocation's were usually not necessary; however, they are
needed even with scoped allocations in some situations - for eg. when the enclosing loop
gets unrolled. The dealloc serves as an end of lifetime marker.

PiperOrigin-RevId: 233653463