xen: Make all performance counter per-cpu, avoiding the need to update

xen: Make all performance counter per-cpu, avoiding the need to update
them with atomic (locked) ops.

Conversion here isn't complete in the sense that many places still use
the old per-CPU accessors (which are now redundant). Since the patch
is already rather big, I'd prefer replacing those in a subsequent
patch.

While doing this, I also converted x86's multicall macros to no longer
require inclusion of asm-offsets.h in the respective C file (on IA64
the use of asm-offsets.h in C sources seems more wide spread, hence
there I rather used IA64_ prefixes for the otherwise conflicting
performance counter indices).

On x86, a few counter increments get moved a little, to avoid
duplicate counting of preempted hypercalls.

Also, a few counters are being added.

IA64 changes only compile-tested, hence somebody doing active IA64
work may want to have a close look at those changes.

Signed-off-by: Jan Beulich <jbeulich@novell.com>