xenoprof: Make the escape code consistent across 32 and 64-bit xen

xenoprof: Make the escape code consistent across 32 and  64-bit xen

At the moment, the xenoprof escape code is defined as "~0UL".
Unfortunately, this expands to 0xffffffff on 32-bit systems
and 0xffffffffffffffff on 64-bit systems; with the result that
while 32-on-32 and 64-in-64 work fine, 32-on-64 (also known as
"compat mode") is broken.

This patch makes the definition consistent across architectures.
In so doing, it will break old-32-bit-on-new-Xen, and vice versa;
but this was seen as an acceptable thing to do.

Signed-off-by: George Dunlap <george.dunlap@eu.citrix.com>
Committed-by: Keir Fraser <keir@xen.org>