ANDROID: GKI: add android_kabi.h

This header file is to be used for various macros to help make keeping
the kernel ABI "stable" during an "ABI Freeze" period.

They are to be used both before the freeze (to anticipate places where
there will be changes), and after the freeze (to keep the abi stable for
structures where there were changes due to LTS or other changes to the
kernel tree.)

Strongly based on rh_kabi.h from Red Hat's RHEL kernel tree.

This adds support for "real" padding and the ability to replace fields
with other fields.

But, note that ABI changes will still be caught by libabigail at this
point in time, work on that is still ongoing.  When that is completed,
all that will be needed is to modify the _ANDROID_KABI_RESERVE() macro
in this file.  No other file changes should be needed.

Bug: 151154716
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: I77038cc251c819c3ed22a9cb8843b185416b6727