test/ring: replace sync with atomic builtins

test/ring: replace sync with atomic builtins

'__sync' built-in functions are deprecated, should use the '__atomic'
built-in instead. the sync built-in functions are full barriers, while
atomic built-in functions offer less restrictive one-way barriers,
which help performance.

Here is the example test result on TX2:
sudo ./arm64-armv8a-linuxapp-gcc/app/test -c 0x7fffffe \
-n 4 --socket-mem=1024,0 --file-prefix=~ -- -i
RTE>>ring_perf_autotest

*** ring_perf_autotest without this patch ***
SP/SC bulk enq/dequeue (size: 8): 6.22
MP/MC bulk enq/dequeue (size: 8): 11.50
SP/SC bulk enq/dequeue (size: 32): 1.85
MP/MC bulk enq/dequeue (size: 32): 2.66

*** ring_perf_autotest with this patch ***
SP/SC bulk enq/dequeue (size: 8): 6.13
MP/MC bulk enq/dequeue (size: 8): 9.83
SP/SC bulk enq/dequeue (size: 32): 1.96
MP/MC bulk enq/dequeue (size: 32): 2.30

So for the ring performance test, this patch improved 11% of ring
operations performance.

Signed-off-by: Phil Yang <phil.yang@arm.com>
Reviewed-by: Gavin Hu <gavin.hu@arm.com>
Reviewed-by: Joyce Kong <joyce.kong@arm.com>
Reviewed-by: Dharmik Thakkar <dharmik.thakkar@arm.com>