FROMLIST: binder: change binder_stats to atomics

(from https://patchwork.kernel.org/patch/9817755/

)

Use atomics for stats to avoid needing to lock for
increments/decrements

Bug: 33250092 32225111
Change-Id: I13e69b7f0485ccf16673e25091455781e1933a98
Signed-off-by: Todd Kjos <tkjos@google.com>