ARM64: Add a README on how to run tests via FVP.

Adds a README file, which describes the steps to build
and run an Android system image targeting the ARM Fixed
Virtual Platform and to use it as a target platform for
running ART tests via ADB.

Test: N/A.
Change-Id: Iaee2ceb6e01ed9d35fbb13755729fc09c99cf21a
1 file changed