kconfig: clarify kvmconfig is for kvm

We'll be adding options for xen as well.

Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Borislav Petkov <bp@suse.de>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Michal Marek <mmarek@suse.cz>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: penberg@kernel.org
Cc: levinsasha928@gmail.com
Cc: mtosatti@redhat.com
Cc: fengguang.wu@intel.com
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: Ian Campbell <Ian.Campbell@citrix.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: xen-devel@lists.xenproject.org
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Acked-by: David Rientjes <rientjes@google.com>
Acked-by: Borislav Petkov <bp@suse.de>
Acked-by: Michal Marek <mmarek@suse.cz>
Signed-off-by: Luis R. Rodriguez <mcgrof@suse.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>