ANDROID: binder: switch task argument for binder_thread

Refactor binder priority functions to take in 'struct binder_thread *'
instead of just 'struct task_struct *'. This allows access to other
thread fields used in subsequent patches. In any case, the same task
reference is still available under thread->task.

There is no functional impact from this patch.

Bug: 148101660
Signed-off-by: Carlos Llamas <cmllamas@google.com>
Change-Id: I67b599884580d957d776500e467827e5035c99f6
(cherry picked from commit 759d9848)