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

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

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

Bug: 151154716
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: Idde3c6e99bd4af3a91ba115b8ec148e3e1cdd4a9