adds LO_FLAGS_AUTOCLEAR for loop device of zram backing device

Userdata spaces leak when zram writeback is enable and repeatedly kill
system_server(restart android).
The reason is that per_boot‘s inode is hold by loop device
although per_boot is deleted by user which become orphan inode in system.

Adds LO_FLAGS_AUTOCLEAR for loop device of zram backing device,
so loop device can release resouce.

Bug: 200904398

Change-Id: Ifeee9c0b58b10cdf7698077fbcaf54d5faccc3b1
Signed-off-by: Liangcai Fan <liangcai.fan@unisoc.com>
Signed-off-by: Hongyu Jin <hongyu.jin@unisoc.com>
Signed-off-by: Jing Xia <jing.xia@unisoc.com>