bus/fslmc: remove conflicting memory barrier macro

bus/fslmc: remove conflicting memory barrier macro

There are two definitions conflicting each other, for more
details, refer to [1].

include/rte_atomic_64.h:19: error: "dmb" redefined [-Werror]
drivers/bus/fslmc/mc/fsl_mc_sys.h:36: note: this is the location of the
previous definition
 #define dmb() {__asm__ __volatile__("" : : : "memory"); }

The fix is to reuse the EAL definition to avoid conflicts.

[1] http://inbox.dpdk.org/users/VI1PR08MB537631AB25F41B8880DCCA988FDF0@
VI1PR08MB5376.eurprd08.prod.outlook.com/T/#u

Fixes: 3af733ba8da8 ("bus/fslmc: introduce MC object functions")
Cc: stable@dpdk.org
Signed-off-by: Gavin Hu <gavin.hu@arm.com>
Reviewed-by: Phil Yang <phil.yang@arm.com>
Acked-by: Hemant Agrawal <hemant.agrawal@nxp.com>