util: provide information whether xlat value has been found

util: provide information whether xlat value has been found

This is necessary for the upcoming change in the output format
of the val3 argument of the FUTEX_WAKE_OP futex command.

* defs.h (printxvals, printxval_searchn): Change return type to int.
(printxval64, printxval, printxval_long): Likewise.  Forward the value
returned by printxvals call.
* util.c (printxvals, printxval_searchn): Change return type to int,
return 1 if xlat value has been found, 0 otherwise.