Revert "x86: Switch QEMU over to use the bochs driver"

Unfortunately the bochs driver does not currently work with distros.
It causes a hang between grub menu selection and the OS displaying
something.

Preliminary investigation shows that GRUB does not jump to the kernel
at all.

This reproduces reliably.

This reverts commit b8956425.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com> # qemu-x86_64
[Slightly modify the commit message about preliminary investigation]
Signed-off-by: Bin Meng <bmeng.cn@gmail.com>