Add options to dmb() and dsb() macros on ARM64

Using plain dsb()/dmb() as full system barriers is usually to much.
Adding proper options to those barriers (instead of full system - sy)
will most likely reduce the cost of the instructions and will benefit
in performance improvement.
This commit adds options to barrier macro definitions.

Obtained from: Semihalf
Reviewed by: andrew, ian
Sponsored by: The FreeBSD Foundation