drm: Remove use of deprecated memory barriers

Replace deprecated smp_mb__*_atomic_inc() memory
barrier API with smp_mb__*_atomic() API. This is
required to avoid build errors.

Change-Id: I15727399a5c24f0188cd2cda76f52aaaedba8a37
Signed-off-by: Deepak Kumar <dkumar@codeaurora.org>