ANDROID: GKI: dma-buf: add dent_count to dma_buf

Partial cherry pick for structure members only.

Signed-off-by: Charan Teja Reddy <charante@codeaurora.org>
(cherry picked from commit cdc117e0)
Signed-off-by: Mark Salyzyn <salyzyn@google.com>
Bug: 157994070
Change-Id: Ie0a833f185687f4cc7ab8189b17fde3516270573
Signed-off-by: Will McVicker <willmcvicker@google.com>