libadf: 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: I14532d59005196e002f7465474ac3c7cc9e59bd3
Signed-off-by: Greg Hackmann <ghackmann@google.com>