binder: separate binder allocator structure from binder proc

The binder allocator is logically separate from the rest
of the binder drivers. Separating the data structures
to prepare for splitting into separate file with separate
locking.

Signed-off-by: Todd Kjos <tkjos@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>