ANDROID: binder: fix KMI-break due to alloc->lock

Wrap 'struct binder_proc' inside 'struct binder_proc_wrap' to add the
alloc->lock equivalent without breaking the KMI. Also, add convenient
apis to access/modify this new spinlock.

Without this patch, the following KMI issues show up:

  type 'struct binder_proc' changed
    byte size changed from 616 to 576

  type 'struct binder_alloc' changed
    byte size changed from 152 to 112
    member 'spinlock_t lock' was added
    member 'struct mutex mutex' was removed

Bug: 254650075
Bug: 319778300
Change-Id: Ic31dc39fb82800a3e47be10a7873cd210f7b60be
Signed-off-by: Carlos Llamas <cmllamas@google.com>