Change flush order in JIT code cache

Flush the data cache before flushing the instruction when dual mapped.

Bug: 62356545
Test: art/test.py -j4 --jit --64 -r --verbose -t test-art-target-run-test-debug-prebuild-jit-no-relocate-ntrace-gcstress-checkjni-picimage-npictest-ndebuggable-no-jvmti-916-obsolete-jit64
Test: Using an Android N image and testing on device from master-art
Change-Id: Ia73da7449cc3a40be0128825233086924eca90a5