tflite: Limit dma_heap ownership to system device

BUG=b:338311947
TEST=CQ

Change-Id: I300a5191af8207d7ca458272325f8693ffacb3d3
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/tflite/+/5836170
Commit-Queue: Jeffrey Kardatzke <jkardatzke@google.com>
Reviewed-by: Shik Chen <shik@chromium.org>
Tested-by: Jeffrey Kardatzke <jkardatzke@google.com>
Reviewed-by: Allen Webb <allenwebb@google.com>