target-arm: add feature flag for ARMv8

Signed-off-by: Mans Rullgard <mans@mansr.com>
target-arm: handle arm-state load acquire/store release instructions

Signed-off-by: Mans Rullgard <mans@mansr.com>
target-arm: handle thumb-state load acquire/store release instructions

Signed-off-by: Mans Rullgard <mans@mansr.com>