tflite: Extract ScopedFd from ahwb

The same ScopedFd RAII helper might be reused by others.

This also simplifies the already lengthy implementation of
hardware_buffer.cc a bit.

BUG=b:305999697
TEST=bazel run --config=host_clang '//android:hardware_buffer_test'

Change-Id: I770c254883423710bd62738edbf3a93987612bba
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/tflite/+/5456233
Tested-by: Shik Chen <shik@chromium.org>
Reviewed-by: Ching-Kang Yen <chingkang@chromium.org>
Commit-Queue: Shik Chen <shik@chromium.org>