binder: implement BINDER_FREEZE ioctl

Frozen tasks can't process binder transactions, so a way is required to
inform transmitting ends of communication failures due to the frozen
state of their receiving counterparts. Additionally, races are possible
between transitions to frozen state and binder transactions enqueued to a
specific process.

Implement BINDER_FREEZE ioctl for user space to inform the binder driver
about the intention to freeze or unfreeze a process. When the ioctl is
called, block the caller until any pending binder transactions toward the
target process are flushed. Return an error to transactions to processes
marked as frozen.

Bug: 143717177
Change-Id: Ie16f72b490bbe1785b82dee2442452f71ad7dc65
Signed-off-by: Marco Ballesio <balejs@google.com>
Co-developed-by: Todd Kjos <tkjos@google.com>