emulator-arm64: ARM64 wrapper for QEMU executable.

This patch adds two new binaries (emulator-arm64 and emulator64-arm64)
which act as a wrapper for QEMU-based emulation engines for ARM64
emulation (and ARM64 _only_).

The (prebuilt) qemu binary must be located under:

  $PROGRAM_DIR/qemu/$SYSTEM/qemu-system-aarch64$EXE

Where:

  $PROGRAM_DIR is the location of the 'emulator-arm64' binary.
  $SYSTEM is a host system tag (e.g. linux-x86 or linux-x86_64)
  $EXE is the host executable extension.

The program is in charge of parsing command-line arguments,
computing AVD configuration, then calling the QEMU program
with a (very long) list of configuration arguments.

See https://qemu-android.googlesource.com/qemu-ranchu/ for
scripts used to rebuild the QEMU prebuilt binary from
sources.

Change-Id: Ifcb9dd50fc5d83a864a1f957d12b1c199e0504fb
7 files changed