ANDROID: dma-buf: Export is_dma_buf_file

Export is_dma_buf_file function which will be used
by several vendors to get dmabuf info.

Bug: 267248830
Bug: 264474028
Change-Id: Ic8f7dd4f0a620839ab19f52841e9a6541515133c
Signed-off-by: Vijayanand Jitta <vjitta@codeaurora.org>
Signed-off-by: T.J. Mercier <tjmercier@google.com>
(cherry picked from commit 409aa4d6)