ANDROID: simplify vendor hooks for non-GKI builds

Vendor hooks required explicitly defining macros or inline functions
to handle the non-GKI build case (!CONFIG_ANDROID_VENDOR_HOOKS). Added
support for generating them automatically so the macros are no longer
required.

Both models are now supported so we can transition.

Bug: 177416721
Signed-off-by: Todd Kjos <tkjos@google.com>
Change-Id: I01acc389d315a5d509b0c48116854342a42e1058