[RAMEN9610-12171] ion: remove recursive lock

[RAMEN9610-12171] ion: remove recursive lock

The oom notifiers is called from alloc_pages when the
memory exhausts. If the ion tries to memory allocation
with acquiring lock, and it happens out-of-memory, and
oom notifiers tries to the same lock, it makes recursive
lock.

Currently, ion_device->buffer_lock, ion_device->lock and
ion_heap->free_lock does not try to allocate memory but
buffer->lock tries to allocate memory, so we remove that
on oom notifier.

If that lock is removed, buffer->iovas and buffer->vaddr,
buffer->kmap_cnt can't be accessed because that requires
the lock to access without any synchronization problem.

Change-Id: Ie85038640d4bd271b28c993017fac865843ed83d
Signed-off-by: hyesoo.yu <hyesoo.yu@samsung.com>