GBE: Consolidate all read/write instruction's bti handling.

GBE: Consolidate all read/write instruction's bti handling.

The previous bti handling for each read/write instruction is
slightly different from each other. There are two major bugs,
the OP_ATOMIC store the bti in different position, so the
post scheduling for ATOMIC instruction is buggy.
The second bug is the DWORD_GATHER instruction is not in
the isRead list. That may cause potential bug.

This patch fixes both of them.

Signed-off-by: Zhigang Gong <zhigang.gong@intel.com>
Reviewed-by: Yang Rong <rong.r.yang@intel.com>