ADF is a modern replacement for fbdev.

ADF's device nodes (/dev/adf[X]), interface nodes
(/dev/adf-interface[X].[Y]), and overlay engine nodes
(/dev/adf-overlay-engine[X].[Y]) are collectively used in similar
contexts as fbdev nodes.  Vendor HW composers (via SurfaceFlinger) and
healthd will need to send R/W ioctls to these nodes to prepare and
update the display.

Ordinary apps should not talk to ADF directly.

Change-Id: Ic0a76b1e82c0cc1e8f240f219928af1783e79343
Signed-off-by: Greg Hackmann <ghackmann@google.com>