x86, cpu: Kill cpu_has_mp

It was used only for checking for some K7s which didn't have MP support,
see

http://www.hardwaresecrets.com/article/How-to-Transform-an-Athlon-XP-into-an-Athlon-MP/24

and it was unconditionally set on 64-bit for no reason. Kill it.

Signed-off-by: Borislav Petkov <bp@suse.de>
Link: http://lkml.kernel.org/r/1403609105-8332-4-git-send-email-bp@alien8.de
Signed-off-by: H. Peter Anvin <hpa@zytor.com>