bionic: move ADF uapi header out of bionic

ADF isn't a candidate for upstreaming and isn't (directly) usable from
unprivileged NDK code, so it makes more sense to keep video/adf.h as a
private header inside libadf, where it'll still be usable by HWC
implementations without shipping in the NDK.

libadf exports its entire include/ directory, so this shouldn't have any
impact on HWC implementations that already link against libadf.

Test: mmm system/core/adf/libadf
Test: /data/nativetest64/adf-unit-tests/adf-unit-tests (on Nexus 9)
Change-Id: I6573f539cfd7fc65433237d0b115b8b7b2728133
Signed-off-by: Greg Hackmann <ghackmann@google.com>