Re-synchronize util.h with XENBUS and use __toupper()

Re-synchronize util.h with XENBUS and use __toupper()

A recent patch introduced __tolower() and __toupper() into util.h as
replacements for tolower() and toupper() respectively as the latter do
a hidden conversion to Unicode which make then unsafe at any IRQL other
than PASSIVE_LEVEL.
This patch imports util.h from XENBUS and fixes other code to be compatible.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>