staging: Android: Add 'vsoc' driver for cuttlefish.

The cuttlefish system is a virtual SoC architecture based on QEMU. It
uses the QEMU ivshmem feature to share memory regions between guest and
host with a custom protocol.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Arve Hjønnevåg <arve@android.com>
Cc: Todd Kjos <tkjos@android.com>
Cc: Martijn Coenen <maco@android.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: devel@driverdev.osuosl.org
Cc: kernel-team@android.com
Signed-off-by: Greg Hartman <ghartman@google.com>
[astrachan: rebased against 4.16, added TODO, fixed checkpatch issues]
Signed-off-by: Alistair Strachan <astrachan@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>