video: adf: replace fbdev helper's open flag with refcount

A device's fb_info is shared between clients.  fb_release() is called
when each client is released, not just the last one.  Since the fbdev
helper needs to release its dma-buf when the last client goes away, it
must keep its own reference count.

fbmem and fbcon hold different locks while calling fb_release(), so
explicit locking is needed.

Change-Id: I42cd659f7633adba7c11f407d4b594bd43305d6a
Signed-off-by: Greg Hackmann <ghackmann@google.com>
Git-commit: e42126fcf1525129f25c895d26ddd868e5d4dff9
Git-repo: https://android.googlesource.com/kernel/common.git


Signed-off-by: Ian Maund <imaund@codeaurora.org>