fflash: Don't depend on system Bazel

The bazel in depot_tools requires either a ChromiumOS checkout
or bazel being installed in the system. Use our own wrapper instead
so fflash can be used when checked out alone

BUG=None
TEST=setup depot_tools
     git clone & checkout
     run ./dev-util/contrib/fflash/fflash --help

Change-Id: Ifb44483392c7b69a9b510ab8164d00e3ce9e702f
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/4835200
Reviewed-by: Ricardo Ribalda <ribalda@chromium.org>
Tested-by: Li-Yu Yu <aaronyu@google.com>
Commit-Queue: Li-Yu Yu <aaronyu@google.com>
5 files changed