Avoid volatile 64-bit tearing on 32-bit architectures.

Change b122a4bbed34ab22b4c1541ee25e5cf22f12a926 removed inline assembly for
volatile 64bit read/writes. This isn't sound in the general case, reinstate.
Motivating change: https://android-review.googlesource.com/91250
Add optimizations for ARM in the case of LPAE support.

Change-Id: Ie86d8885d27c8f0da75f0c3bd50d4553a331282f
2 files changed