ANDROID: GKI: kernfs.h: add Android ABI padding to some structures

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

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

Bug: 151154716
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: I1fcb0b81c3ea7d5300da283b275391f95d6d4ec8