Add '-accel <mode>' and 'no-accel' options.

This patch adds two new options to better control CPU emulation
acceleration (i.e. KVM and HAX). More specifically:

  '-no-accel' can be used to disable acceleration if available.
  '-accel off' does the same.
  '-accel on' forces to run with acceleration, or refuses to start
  the emulator.
  '-accel auto' probes the system for a working accelerator and uses
  it when possible (i.e. when emulating x86 or x86_64 images only).

Also print some information with -verbose or -debug-init.

Note: This adds QEMU-independent probing code for KVM and HAX
      under android/emulation/ (C++), as well as some glue to
      use it from C under android/cpu_accelerator.[hc].

Note: HAX is no longer enabled by default when reaching the QEMU
      main function.

Change-Id: Ic91db7a3b213d69296c50fec35cd29a32a8e5779
diff --git a/vl-android.c b/vl-android.c
index 87cb06b..be33559 100644
--- a/vl-android.c
+++ b/vl-android.c
@@ -295,7 +295,7 @@
 const char *vnc_display;
 int acpi_enabled = 1;
 int no_hpet = 0;
-int hax_disabled = 0;
+int hax_disabled = 1;
 int no_virtio_balloon = 0;
 int fd_bootchk = 1;
 int no_reboot = 0;
@@ -3068,9 +3068,14 @@
                 break;
 
 #endif
+#ifdef CONFIG_HAX
+            case QEMU_OPTION_enable_hax:
+                hax_disabled = 0;
+                break;
             case QEMU_OPTION_disable_hax:
                 hax_disabled = 1;
                 break;
+#endif
             case QEMU_OPTION_android_ports:
                 android_op_ports = (char*)optarg;
                 break;