FROMLIST: android: binder: Don't get mm from task

(from https://patchwork.kernel.org/patch/9954125/

)

Use binder_alloc struct's mm_struct rather than getting
a reference to the mm struct through get_task_mm to
avoid a potential deadlock between lru lock, task lock and
dentry lock, since a thread can be holding the task lock
and the dentry lock while trying to acquire the lru lock.

Test: ran binderLibTest, throughputtest, interfacetest and
mempressure w/lockdep
Bug: 63926541
Change-Id: Icc661404eb7a4a2ecc5234b1bf8f0104665f9b45
Acked-by: Arve Hjønnevåg <arve@android.com>
Signed-off-by: Sherry Yang <sherryy@android.com>