FROMLIST: binder: don't modify thread->looper from other threads

(from https://patchwork.kernel.org/patch/9817799/

)

The looper member of struct binder_thread is a bitmask
of control bits. All of the existing bits are modified
by the affected thread except for BINDER_LOOPER_STATE_NEED_RETURN
which can be modified in binder_deferred_flush() by
another thread.

To avoid adding a spinlock around all read-mod-writes to
modify a bit, the BINDER_LOOPER_STATE_NEED_RETURN flag
is replaced by a separate field in struct binder_thread.

Change-Id: I92a5d084081e813b6d8c60f970dd58cc031042d6
Signed-off-by: Todd Kjos <tkjos@google.com>