Update to fix ADB disconnection issues.

This updates the emulator binaries to include a fix for an issue
where emulator would not be properly visible to 'adb devices' after
the ADB server process is killed / disconnected.

    $ cd external/qemu && git log --oneline --no-merges ef4b60f..6b3cbff .
        6b3cbff Fixes emulator and adb server disconnect issue
        cbe657d TCG: Update to QEMU 2.0.0 version.
        fa22f46 android-configure.sh: Use GCC 4.8 on Linux.
        36c80b3 Force network port for adb qemu communication.
        4050560 Disable the adb qemud pipe by default.
        2944ca1 Properly reset the value of max_fd when it becomes invalid.
        7b5c578 Fixed network access in windows emulator
        9e4a448 build-kernel.sh: Make --arch=arm64 build ranchu version by default.

Change-Id: I4b169813ec6366b903f44889c2aa8cb257a8abd2
Add linux qemu-system-aarch64 binary.

This patch adds the linux-x86_64 binary required to emulate ARM64
properly, using binaries built from qemu-android.

Rebuild instructions:

  AOSP=/path/to/aosp
  EMULATOR_PREBUILTS=$AOSP/prebuilts/android-emulator
  cd /tmp
  git clone https://qemu-android.googlesource.com/qemu-android
  git clone https://qemu-android.googlesource.com/qemu-ranchu

  qemu-ranchu/scripts/rebuild.sh /tmp/qemu-android $AOSP
  mkdir $EMULATOR_PREBUILTS/qemu
  cp -r /tmp/qemu-ranchu/binaries/linux-x86_64 $EMULATOR_PREBUILTS/qemu/

NOTE: The binary is picked up automatically by the 'emulator' binary
      when the target AVD uses the arm64-v8a ABI (or arm64 CPU).

Change-Id: Ibfe5831ec20119f37938f96f24f33907402297d1
Update: use 1GB minimum RAM for ARM64 emulation.

Change-Id: If847ae44685e44967a20c0ffc074acb65b6f05a0
arm64: Fix arm64 launcher to work with '-memory <number>'

Change-Id: Ic815eead7b310046e642cc0d20f7984925dc1135
Update prebuilt emulator binaries.

    $ cd external/qemu && git log --oneline --no-merges e23bd74..509afff .
        509afff Use prebuilt toolchain for Darwin builds.
        4a7d6ec android/base/HashUtils.h: Remove compiler error.
        6c28cf5 output version of gcc during emulator configure
        9572bb3 linux: Fix timezone detection code.
        539397e Fix issue #75221: Skip all response headers from HTTP Proxy.
        820b4f2 Ensure 'emulator' launcher is always built on Darwin.
        3afa556 using pc-bios files from prebuilts/qemu-kernel
        6bd665a emulator: Refuse to run 32-bit Linux binaries by default.
        f492dec Makefile.android: Remove 32-bit binaries on Darwin.
        c9993fb emulator release script: incl. windows, 32bit linux binaries
        8cc1912 Switched from prebuilt emulator binaries to built binaries
        0802e66 remove 32bit emulator binaries from OSX SDK
        5a646cd Increase TCG_MAX_TEMPS from 512 to 1024.
        aed26c6 Set num_clients appropriately when loading from a snapshot
        d155d3f Fix ScopedSocket unittest.
        e09cde4 package-release.sh: Add --debug flag.
        1dd4a03 SocketUtils.cpp: Fix Windows implementation.
        0935940 android/base/Log.h: Add DPLOG() and DPLOG_IF()
        c63d57d package-release.sh can’t copy emulator binaries from darwin
        c0294a6 Fix package-release.sh
        ba6c712 Fix timer bug

    $ cd sdk/emulator/opengl && git log --oneline --no-merges 1ee821e..31435b2 .
        31435b2 emulator/opengl: Cleanup build files + remove obsolete tests.

Change-Id: I7315ba15f856c6d51d86c79e940c46eb32dd7e3a