GBE: work around the local memory barrier fence issue.
GBE: work around the local memory barrier fence issue.

According to the spec, we do not need to add a memory fence
for SLM's access. But, in pratice, we have to add it to make
sure get correct result. Don't know the root cause yet, just
use this work around now.

Signed-off-by: Zhigang Gong <e04a7b9b70b1e4c6318cf117dcd1a9056e14b97a@linux.intel.com>

zhenyw/beignet,zhenyw/beignet,freedesktop-unofficial-mirror/beignet,ignatenkobrain/beignet,zhenyw/beignet,freedesktop-unofficial-mirror/beignet,zhenyw/beignet,wdv4758h/beignet,ignatenkobrain/beignet,ignatenkobrain/beignet,wdv4758h/beignet,wdv4758h/beignet,zhenyw/beignet,ignatenkobrain/beignet,ignatenkobrain/beignet,freedesktop-unofficial-mirror/beignet,wdv4758h/beignet,wdv4758h/beignet,freedesktop-unofficial-mirror/beignet