Warn/Panic with x86_64 emulation without CPU acceleration.

x86_64 emulation currently requires KVM/HAX, i.e. trying to boot
with -no-accel will not work at all. This is a bug that hasn't
been widely documented yet, and has burnt a few people, so add
a check that will:

  - Panic at startup when trying to emulator an x86_64 AVD
    without proper CPU acceleration.

  - If -no-accel of '-accel off' is used explicitly though,
    just print a warning. Might be useful for debugging the
    issue itself.

BUG=15445856

Change-Id: Ifb565bd95926a9534087187bc2d1dc425a854d67
1 file changed