x86: Switch QEMU over to use the bochs driver

This is more convenient since it does not require a video BIOS. Enable
it for QEMU.

Also drop use of video in SPL for the 64-bit QEMU, since it not needed
now.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>