ANDROID: GKI: elevator: add Android ABI padding to some structures

Try to mitigate potential future driver core api changes by adding a
padding to struct elevator_mq_ops and struct elevator_type.

Based on a change made to the RHEL/CENTOS 8 kernel.

Bug: 151154716
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: Ia4c2667fd5ca9e6dd2e0d30b95a0f8d5eb7921dc