vl: convert -smp to qemu_opts_parse()

This also introduces a new suboption, "cpus=",
which is the default.  So after this patch,

 -smp n,sockets=y

is the same as

  -smp cpus=n,sockets=y

(with "cpu" being some generic thing, referring to
either cores, or threads, or sockets, as before).

We still don't validate relations between different
numbers, for example it is still possible to say

  -smp 1,sockets=10

and it will be accepted to mean sockets=1.

Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
Message-id: 1372072012-30305-1-git-send-email-mjt@msgid.tls.msk.ru
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
