Add BINDER_GET_NODE_DEBUG_INFO ioctl

The BINDER_GET_NODE_DEBUG_INFO ioctl will return debug info on
a node.  Each successive call reusing the previous return value
will return the next node.  The data will be used by
libmemunreachable to mark the pointers with kernel references
as reachable.

Bug: 28275695
Change-Id: Idbbafa648a33822dc023862cd92b51a595cf7c1c
Signed-off-by: Colin Cross <ccross@android.com>
Signed-off-by: Martijn Coenen <maco@android.com>