procrank: prefer new zram ABI

Starting with Linux 4.1, reading from /dev/block/zram*/mem_used_total
logs this warning:

"Attribute mem_used_total (and others) will be removed. See zram
documentation."

mem_used_total and several related counters are now consolidated under a
new node mm_stat.  Prefer that when it's available.

Bug: 25951511

Change-Id: Ida732ee56a1e39e01c390f61bb40b3f52f643004
Signed-off-by: Greg Hackmann <ghackmann@google.com>
1 file changed