android: drivers: workaround debugfs race in binder

android: drivers: workaround debugfs race in binder

If a /d/binder/proc/[pid] entry is kept open after linux has
torn down the associated process, binder_proc_show can deference
an invalid binder_proc that has been stashed in the debugfs
inode.  Validate that the binder_proc ptr passed into binder_proc_show
has not been freed by looking for it within the global process list
whilst the global lock is held. If the ptr is not valid, print nothing.

Bug: 19587483

Change-Id: Idd5ad79f5648b7eed49d1ec75ae93f9e12a74ee9
Signed-off-by: Dmitry Shmidt <dimitrysh@google.com>