x86: consolidate/enhance TLB flushing interface

x86: consolidate/enhance TLB flushing interface

Folding into a single local handler and a single SMP multiplexor as
well as adding capability to also flush caches through the same
interfaces (a subsequent patch will make use of this).

Once at changing cpuinfo_x86, this patch also removes several unused
fields apparently inherited from Linux.

Signed-off-by: Jan Beulich <jbeulich@novell.com>
Signed-off-by: Keir Fraser <keir@xensource.com>