[x86 setup] Present the canonical video mode number to the kernel

Canonicalize the video mode number as presented to the kernel.  The
video mode number may be user-entered (e.g. ASK_VGA), an alias
(e.g. NORMAL_VGA), or a size specification, and that confuses the
suspend wakeup code.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>