ARM64: Restore FP registers in read barrier thunk.

bug: 62612946
Test: 658-fp-read-barrier
Test: run-libcore-tests.sh

(cherry picked from commit 7015e76436ff9eb738c9c6070c8fff8e98b3852e)

Change-Id: Id0bc55c21829429cd17a77e4c503971249c107f5
(cherry picked from commit a77f3c91ad7bd46fff8e98f582eef216892219b9)
4 files changed