Dalvik: DMB Optimisation

Replaces use of 'dmb' and 'dmb st' with inner-shareable versions.
This should improve performance in certain cases without harming
correctness.

Change-Id: Id30f58b93b34bf0e232bb01dc3956a82f7a69c40
(cherry picked from commit 2ea163ba54731afcfa11341a525c33e08d0781fa)